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{{Short description|Totality of existing entities}}
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'''Reality''' is the totality of [[existence]] or what all existing entities have in common. It is often contrasted with [[Phenomenon|appearance]], opposing what is with what seems to be, although the accuracy and fundamentality of this contrast are disputed. Various criteria for distinguishing real from unreal entities have been proposed, including [[Causality|causal]] powers, mind-independence, and being non-[[Illusion|illusory]]. The concept of ''reality'' overlaps with notions such as being, existence, [[world]], [[actuality]], and [[truth]].

Debates about the constituents and structure of reality ask [[Categories of being|what kinds of things there]] are and how they are organized. Proposed constituents include [[particulars]] and [[universals]], [[Abstract and concrete|concrete and abstract objects]], [[facts]], [[Event (philosophy)|events]], and [[elementary particles]]. Structural questions address the [[Mereology|relation between parts and wholes]], the distinction between fundamental and non-fundamental entities, the idea that reality forms a hierarchy of levels, and the roles of unity and multiplicity in [[Monism|monist]]–[[Pluralism (philosophy)|pluralist]] debates. Other discussions examine [[space]] and [[time]] as frameworks that organize [[Relation (philosophy)|relations]] among entities, and [[Scientific law|laws of nature]] describing regularities or general patterns of how entities interact and changes unfold.

[[Philosophical realism|Realism]] is the view that reality does not depend on human [[knowledge]] or [[consciousness]] and exists apart from them. [[Anti-realism]], by contrast, holds that certain aspects of reality depend on [[mental processes]], [[Subjectivity|subjective]] perspectives, or social conventions. Debates between realists and anti-realists span multiple domains, addressing the objective existence of universals, abstract objects, [[values]], and [[unobservable]] entities posited by scientific theories. A related topic concerns the possibility and limits of knowledge as a successful cognitive contact with reality. Contemporary technology in the form of [[augmented reality|augmented]] and [[virtual reality]] can inform experience and raises questions about the [[ontological]] status of [[Virtual artifact|virtual objects]].

The concept of reality is relevant to many fields, including [[metaphysics]], [[epistemology]], [[physics]], [[psychology]], and [[anthropology]]. Theories of the nature of reality have been discussed since [[Ancient history|antiquity]] and continue to shape contemporary inquiry, with influential early traditions originating in ancient [[Indian philosophy|Indian]], [[Ancient Chinese philosophy|Chinese]], and [[Ancient Greek philosophy|Greek thought]].

== Definition ==
Reality is the totality of existing [[Entity|entities]]. It encompasses the whole [[cosmos]] and [[everything]] within it, including rocks, trees, humans, and stars. In a slightly different sense, reality is not the totality itself but an aspect shared by all its constituents. In this sense, it is the state of being real or what all real entities have in common, separating them from unreal or [[Illusion|illusory]] ones. When used as a [[countable noun]], the expression ''a reality'' denotes a specific domain or coherent, interconnected framework, such as the [[social reality]] of a particular [[culture]] or the [[virtual reality]] of a specific [[video game]] world.<ref>{{multiref | {{harvnb|Chalmers|2022|loc=§ 6. What Is Reality?}} | {{harvnb|HarperCollins|2022}} | {{harvnb|Penrose|2006|pp=32–34}} | {{harvnb|Bunge|2006|pp=[https://books.google.com/books?id=6GraKxazuOQC&pg=PA27 27–28]}} | {{harvnb|Cambridge University Press & Assessment|2026}} }}</ref>

Reality is often contrasted with [[Phenomenon|appearance]]: appearance is how things seem to be, while reality is how they in fact are. It is controversial whether this contrast marks a genuine and fundamental difference between an experienced realm of appearances and an [[Noumenon|inaccessible realm]] of reality. Another outlook holds that appearance and reality are different ways of considering the same being, locating the difference in the conceptual framing rather than a division of worlds. This view is consistent with the idea that accurate appearances show things as they are, suggesting that appearance and reality can align and are not necessarily distinct. Both accurate and inaccurate appearances may themselves be part of reality, for instance as brain events, according to one suggestion.<ref>{{multiref | {{harvnb|Rescher|2010|pp=1–7, 16}} | {{harvnb|Wilson|2005|pp=43–44}} | {{harvnb|Kennick|2006|loc=Lead section, § Looks and Appearances}} | {{harvnb|Bunge|2006|pp=[https://books.google.com/books?id=6GraKxazuOQC&pg=PA6 6–8, 23]}} }}</ref> Real entities are typically taken to exist on their own, independent of what people think about them. When a person encounters them, their appearances may reveal only some features while leaving others hidden. Whereas appearances can be [[Vagueness|vague]], as in a [[blurry vision]], it is often suggested that reality is fully [[determinate]] or fixed in all details.<ref>{{multiref | {{harvnb|Rescher|2010|pp=7–10}} | {{harvnb|Searle|1998|p=398}} | {{harvnb|Bunge|2006|pp=[https://books.google.com/books?id=6GraKxazuOQC&pg=PA27 27–28]}} | {{harvnb|Rescher|2018|pp=[https://books.google.com/books?id=jVyAEQAAQBAJ&pg=PA1 1–4]}} }}</ref>

The word ''reality'' comes from the [[Latin]] term {{lang|la|realitas}}, rooted in the word {{lang|la|res}}, meaning {{gloss|thing}}, and from the [[French language|French]] term {{lang|fr|réalité}}. Its earliest known use in English dates to the early 1500s.<ref>{{multiref | {{harvnb|OED staff|2026}} | {{harvnb|Chantrell|2002|p=419}} | {{harvnb|Rescher|2018|p=[https://books.google.com/books?id=jVyAEQAAQBAJ&pg=PA1 1]}} }}</ref> The concept of reality is relevant to many fields, including [[metaphysics]], a branch of [[philosophy]] that studies the nature and fundamental structure of reality, and the [[empirical sciences]], which examine the constituents and [[Scientific law|laws of the natural world]] through [[observation]] and [[experimentation]].<ref>{{multiref | {{harvnb|Koons|Pickavance|2017|p=[https://books.google.com/books?id=FLH4DQAAQBAJ&pg=PA3 3–4, 7]}} | {{harvnb|Penrose|2006|pp=32–34}} | {{harvnb|Rescher|2018|pp=[https://books.google.com/books?id=jVyAEQAAQBAJ&pg=PR7 vii, ix–x]}} }}</ref>

=== Criteria ===
Criteria of reality are proposed features or standards that distinguish real entities from unreal ones.<ref>{{multiref | {{harvnb|Wilson|2005|pp=43–44}} | {{harvnb|Chalmers|2022|loc=§ 6. What Is Reality?}} }}</ref> An often-cited criterion identifies [[Causality|causal]] powers as the mark of reality. Discussed in [[ancient Greek philosophy]] as the [[Eleatic principle]], it states that to be real is to be able to produce changes and to be affected by them. For example, [[Mahatma Gandhi]] was real because he was able to mobilize millions and shape [[Indian independence movement|India's struggle for independence]]. [[Santa Claus]], by contrast, is unreal because he cannot act upon the world. However, stories about Santa Claus, such as written texts in children's books, are part of reality since they can influence how people think. The Eleatic principle is controversial because it is typically taken to deny that abstract objects studied in fields like [[mathematics]], such as [[number]]s, are real.<ref>{{multiref | {{harvnb|Chalmers|2022|loc=§ 6. What Is Reality?}} | {{harvnb|Rescher|2010|p=8}} | {{harvnb|Campbell|2006|loc=§ Being Qua Being}} }}</ref>

Another influential proposal treats mind-independence as a criterion of reality, arguing that real entities do not depend on how people think about them. This view emphasizes that reality is encountered, rather than invented, and can resist or frustrate beliefs and desires, unlike malleable [[Imagination|imaginary]] creations. For example, if a planet or a virus is real then it exists on its own and behaves according to its nature, even if people are unaware or hold false beliefs about it. Unreal entities, by contrast, depend for their existence on thoughts and ideas; they would not arise or would vanish without the mental activity creating or sustaining them. For instance, a [[fictional character]] like [[Gandalf]] would not be there if no one had ever thought about him. A difficulty for this criterion is to account for the reality of mental entities themselves, given that [[thoughts]], [[memories]], and [[emotions]] seem to be part of the world.<ref>{{multiref | {{harvnb|Chalmers|2022|loc=§ 6. What Is Reality?}} | {{harvnb|Rescher|2010|pp=9–10}} | {{harvnb|Bunge|2006|pp=[https://books.google.com/books?id=6GraKxazuOQC&pg=PA27 27–28]}} }}</ref>

A closely related criterion holds that to be real is to be non-illusory. It focuses on how things seem to be, distinguishing real appearances, which are as they seem, from illusory ones, which are not as they seem. In a broad sense, appearances are not limited to what people perceive but can also include memories, beliefs, and thoughts. According to this criterion, veridical [[perception]]s track reality by presenting it as it is, whereas entities found in [[hallucinations]], [[dreams]], and [[mirage]]s count as unreal because they misrepresent the world.<ref>{{multiref | {{harvnb|Chalmers|2022|loc=§ 6. What Is Reality?}} | {{harvnb|Bunge|2006|pp=[https://books.google.com/books?id=6GraKxazuOQC&pg=PA6 6–8, 23]}} | {{harvnb|Wilson|2005|pp=43–44}} }}</ref>

A different criterion equates reality with being genuine. Proposed by [[J. L. Austin]] and grounded in [[ordinary language philosophy]], it suggests that being real is always relative to a category or entity, such as a real diamond. This view contrasts being real with being fake, like the distinction between a real [[duck]] and a fake one used as a [[decoy]]. A challenge for approaches grounded in ordinary language is that the term ''real'' serves many linguistic purposes, not all of which are relevant to the metaphysical concept of reality. For example, it can express that something is excellent relative to its kind, as in the exclamation "Now this is real coffee!"<ref>{{multiref | {{harvnb|Chalmers|2022|loc=§ 6. What Is Reality?}} | {{harvnb|Bennett|1966|pp=501–504}} | {{harvnb|Reynolds|2006|pp=468–469, 476–479}} }}</ref>

Other suggested criteria identify reality with what is [[observable]], [[measurable]],{{efn|Measurability plays a key role in scientific conceptions of reality.<ref>{{harvnb|Horák|Rott|2003|pp=1–12}}</ref>}} coherent,{{efn|For example, philosophers such as [[Zeno of Elea]] and [[F. H. Bradley]] have argued that certain phenomena, like [[time]] and [[motion]], are unreal because they are incoherent or paradoxical.<ref>{{multiref | {{harvnb|Kennick|2006|loc=§ Appearances of the Impossible}} | {{harvnb|Wilson|2005|pp=43–44}} }}</ref>}} useful, [[Subjectivity and objectivity (philosophy)|objective]], [[intersubjective]], or fundamental.<ref>{{multiref | {{harvnb|Chalmers|2022|loc=Footnote 115}} | {{harvnb|Rescher|2010|pp=8–10}} | {{harvnb|Wilson|2005|pp=43–44}} }}</ref>

=== Related concepts ===
[[File:Alexius Meinong 1900.jpg|alt=Photo of a bearded man wearing a suit|thumb|upright=.8|According to [[Alexius Meinong]], the concept of being is broader than the concept of reality since it also encompasses nonexistent objects.<ref>{{harvnb|Marek|2024|loc=Lead section, § 2. Meinong on Philosophy, § 5. Object Theory — Ontology beyond Being and Non-Being}}</ref>]]
The term ''reality'' overlaps with various related concepts, such as being, [[existence]], [[world]], [[actuality]], and [[truth]]. Depending on the context, these terms may function as synonyms or play distinct theoretical roles.<ref>{{multiref | {{harvnb|Rescher|2018|pp=[https://books.google.com/books?id=jVyAEQAAQBAJ&pg=PA1 1]}} | {{harvnb|HarperCollins|2022}} | {{harvnb|Campbell|2006|loc=Lead section, § Reality and Actuality}} }}</ref> In the broadest sense, being is the most general category that applies to everything and contrasts only with [[nothingness]].<ref>{{multiref | {{harvnb|MacIntyre|2006|loc=Lead section, § 'Being' as a Name}} | {{harvnb|Jaroszyński|2023|pp=[https://books.google.com/books?id=LtL7EAAAQBAJ&pg=PA254 254–255]}} | {{harvnb|Lowe|2005|p=84}} | {{harvnb|Jacquette|2014|pp=[https://books.google.com/books?id=NmPfBQAAQBAJ&pg=PA1 1–2, 12–13]}} }}</ref> Some philosophers, such as [[Alexius Meinong]], hold that being is a broader concept than reality, encompassing nonexistent objects, such as merely possible or incomplete objects, in addition to real or actual ones.<ref>{{harvnb|Marek|2024|loc=Lead section, § 2. Meinong on Philosophy, § 5. Object Theory — Ontology beyond Being and Non-Being}}</ref> In a narrow sense, being contrasts with [[Becoming (philosophy)|becoming]], and denotes stable or permanent aspects of reality. Becoming, by contrast, covers change, like when an entity shifts from one state of being to another.<ref>{{multiref | {{harvnb|MacIntyre|2006|loc=Lead section, § 'Being' as a Name}} | {{harvnb|Zhang|2011|p=[https://books.google.com/books?id=Vl4EEAAAQBAJ&pg=PA220 220]}} | {{harvnb|Hartmann|2012|pp=[https://books.google.com/books?id=4PyJfVZn-rcC&pg=PA46 46–47]}} }}</ref> A central topic in ontology is the [[categories of being]]{{em dash}}fundamental classes that map out a comprehensive inventory of reality.<ref>{{harvnb|Campbell|2006|loc=§ The Categories of Being}}</ref>

Existence is commonly understood as the bare fact that something is, indicating that an entity is part of the world without specifying its nature. It is often contrasted with [[essence]], which denotes the nature or characteristic features of an entity. It is frequently possible to understand the essence of something without knowing whether it exists. Ontologists discuss whether existence can be understood as a property of [[Particular|individuals]], analogous to ordinary features like being red, or whether it is instead a concept or [[Quantifier (logic)|quantificational]] device expressing that a property has instances.<ref>{{multiref | {{harvnb|Gibson|1998|p=2}} | {{harvnb|Ceylan|1993|pp=[https://www.jstor.org/stable/20840134 329–337]}} | {{harvnb|Nelson|2022|loc=Lead Section}} | {{harvnb|MacIntyre|2006|loc=§ Is Existence a Predicate?}} }}</ref>

A world is a totality of entities, conceived as a maximally large situation or a system encompassing everything in space and time as a whole: all that was, is, and will be.<ref>{{multiref | {{harvnb|Menzel|2025|loc=Lead section}} | {{harvnb|Bunge|2006|pp=[https://books.google.com/books?id=6GraKxazuOQC&pg=PA20 20–21]}} }}</ref> Some philosophers hold that reality consists of only one world: the actual universe. A different view suggests that reality is made up of many worlds that exist in parallel to one another, each representing a distinct way of how things could have been. For example, [[David Lewis (philosopher)|David Lewis]]'s [[modal realism]] asserts that there exist countless spatiotemporally unified [[possible worlds]], each just as real as the actual world.<ref>{{multiref | {{harvnb|Menzel|2025|loc=§ 2. Three Philosophical Conceptions of Possible Worlds}} | {{harvnb|Parent|loc=Lead section, § 2. Lewis' Realism}} }}</ref> Similarly, the [[many-worlds interpretation]] of [[quantum physics]] suggests that in [[Measurement in quantum mechanics|quantum measurements]], not only one but all possible outcomes occur, interpreted as a branching of the universe into multiple worlds.<ref>{{harvnb|Vaidman|2021|loc=Lead section, § 1. Introduction}}</ref>

Actuality encompasses the states of entities that are realized or manifested. It contrasts with potentiality, which denotes [[dispositions]] an entity has but does not exercise. For example, an [[acorn]] has the potential to grow into an [[oak tree]] under the right conditions, but the oak tree is not yet actualized.<ref>{{multiref | {{harvnb|Feser|2017|pp=35–38}} | {{harvnb|Rée|Urmson|2004|pp=30–31}} | {{harvnb|Campbell|2006|loc=§ Reality and Actuality}} }}</ref> In a slightly different sense, actuality is often discussed in relation to possibility and necessity as different modes of being. Actuality comprises what is the case, possibility denotes what could be the case, and necessity concerns what must be the case.<ref>{{multiref | {{harvnb|Rescher|2010|p=7}} | {{harvnb|Hartmann|2013|pp=[https://books.google.com/books?id=sL-lJxW_swAC&pg=PA1 1–5]}} | {{harvnb|Horák|Rott|2003|pp=1–2}} }}</ref> The distinction is often framed in terms of possible worlds: a state is possible if it holds in at least one possible world; it is actual if it holds in the actual world; and it is necessary if it holds in all possible worlds.<ref>{{multiref | {{harvnb|Menzel|2025|loc=Lead Section, § 1. Possible Worlds and Modal Logic}} | {{harvnb|Kuhn|2010|p=[https://books.google.com/books?id=c_eYe6NVaDMC&pg=PA13 13]}} }}</ref> While actuality and necessity are often treated as aspects of reality, there are debates about the extent to which possibilities are part of it, for example, regarding the contrast between real or authentic possibilities and formal or inauthentic ones.<ref>{{multiref | {{harvnb|Rescher|2010|pp=6–7}} | {{harvnb|Horák|Rott|2003|pp=1–2}} | {{harvnb|Gibbs|1970|pp=340–341}} }}</ref>

Truth is conformity to reality. It contrasts with [[falsehood]], which encompasses misrepresentations that do not align with reality. Truth is often understood as a [[Property (philosophy)|property]] of [[Proposition|statements]] or beliefs that describe the world as it is.<ref>{{multiref | {{harvnb|Simmons|2006|p=534–535}} | {{harvnb|Glanzberg|2018|pp=1–3}} | {{harvnb|Beall|Middleton|2024|pp=6–7}} }}</ref> In this sense, truth is not the same as reality but a feature of accurate representations of it: truth depends on reality.<ref>{{multiref | {{harvnb|Rescher|2010|pp=12–14}} | {{harvnb|Asay|2020|pp=[https://books.google.com/books?id=Y13bDwAAQBAJ&pg=PA1 1–2]}} }}</ref> In a different sense, the term ''truth'' is used as a synonym for reality, as in the statement "In truth, he was not qualified for the job."<ref>{{harvnb|HarperCollins|2022a}}</ref> Various [[Theories of truth|theories of the nature of truth]] have been proposed. According to [[Correspondence theory of truth|correspondence theory]], a statement is true if it corresponds to facts. The [[Coherence theory of truth|coherence theory]] suggests that truth consists in logical consistency and mutual support among beliefs. [[Pragmatic theory of truth|Pragmatic theories]] define truth relative to consequences, holding that truth is what works or what would withstand the test of unlimited inquiry. [[Deflationary theory of truth|Deflationary theories]] hold that truth has no significant intrinsic nature beyond its minimal linguistic role in truth-related expressions.<ref>{{multiref | {{harvnb|Glanzberg|2025|loc=§ 1. The Neo-Classical Theories of Truth, § 5. Deflationism}} | {{harvnb|Engel|2002|pp=12–15, 26–27, 34–35, 41–42}} }}</ref>

== Constituents ==
Various [[categories of being]] or constituents of reality are discussed in the academic discourse. There are disagreements about which exist at the most fundamental level and whether reality is ultimately composed of one or several types.<ref>{{multiref | {{harvnb|Campbell|2006|loc=§ The Categories of Being}} | {{harvnb|Bunge|2006|pp=[https://books.google.com/books?id=6GraKxazuOQC&pg=PA27 27–28, 74]}} | {{harvnb|Thomasson|2022|loc=Lead Section}} }}</ref>

A central distinction is between [[particular]]s and [[universals]]. Particulars are unique, non-repeatable entities, such as [[Julius Caesar]], the [[river Nile]], and [[the Moon]]. As individual entities, they contrast with universals, which are general, repeatable entities that can have many instances, such as the color blue, the shape roundness, and the property of being a [[mammal]]. Particulars are often characterized as entities that instantiate universals but are not themselves instantiated by anything else. In this sense, they exist in themselves, while universals exist in something else.<ref>{{multiref | {{harvnb|Loux|Crisp|2017|pp=17–19, 82–83}} | {{harvnb|Maurin|2019|loc=Lead Section}} | {{harvnb|Bigelow|1998|loc=Lead Section}} | {{harvnb|Cowling|2019|loc=Lead Section}} }}</ref>

Universals are often analyzed in terms of [[Property (philosophy)|properties]]{{efn|[[Trope theory]] offers an alternative view by treating properties as particularized instances, called ''tropes''.<ref>{{multiref | {{harvnb|Maurin|2024}} | {{harvnb|Orilia|Paolini Paoletti|2022|loc=§ 1.6 Universals versus Tropes}} }}</ref>}} and [[Relation (philosophy)|relations]]. A property expresses a characteristic or quality of another entity. For example, roundness is a property of the particulars the Moon and [[the Sun]]. Relations are ways in which two or more entities stand to one another. For instance, being-smaller-than is a relation that holds between the Moon and the Sun.<ref>{{multiref | {{harvnb|Campbell|2006|loc=§ Properties and Relations}} | {{harvnb|Orilia|Paolini Paoletti|2022|loc=Lead Section, § 1.5 Relations}} | {{harvnb|Sider|2010|p=[https://books.google.com/books?id=-KkPEAAAQBAJ&pg=PA13 13]}}}}</ref> One approach analyzes the instantiation of universals in terms of [[fact]]s or [[State of affairs (philosophy)|states of affairs]]. For example, the fact "Socrates is mortal" has two components: the particular ''Socrates'' and the universal ''mortality''. [[Event (philosophy)|Events]] are proposed constituents of reality that occur in time, such as the [[discovery of penicillin]] and the [[Second World War]].<ref>{{multiref | {{harvnb|Campbell|2006|loc=§ Complexes}} | {{harvnb|Loux|Crisp|2017|pp=139–145}} | {{harvnb|Armstrong|2010|pp=26–30}} }}</ref>

[[File:(Venice) Aristotele by Francesco Hayez in gallerie Accademia Venice (cropped).jpg|thumb|alt=Oil painting of a bearded man in robes|[[Aristotle]] proposed a system of ten categories to describe the fundamental constituents of reality.<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.1 Aristotelian Realism}} | {{harvnb|Studtmann|2024|loc=§ 2. The Ten-Fold Division}} | {{harvnb|Wardy|1998|loc=§ 1. Categories in Aristotle}} }}</ref>]]

Another influential distinction is between [[Abstract and concrete|concrete and abstract]] objects. According to a common view, concrete objects exist in space and time, such as a flower, a horse, and a ship. They can undergo changes, have causal powers, and influence each other, like when a horse eats a flower and destroys it in the process. Abstract objects lack spatiotemporal location, do not change, and have neither causes nor effects,{{efn|The exact definition of abstract objects is disputed.<ref>{{harvnb|Oliver|2005|p=3}}</ref>}} such as mathematical [[number]]s and geometrical [[shape]]s. It is disputed whether abstract objects are fundamental constituents of reality or merely conceptual constructions.<ref>{{multiref | {{harvnb|Armstrong|2010|pp=1–2, 5, 8}} | {{harvnb|Campbell|2006|loc=§ Abstract Objects}} | {{harvnb|Oliver|2005|p=3}} }}</ref>

Philosophers have proposed various theories of categories. [[Aristotle]] developed [[Categories (Aristotle)|a system of ten categories]], which has [[Substance theory|substance]] as the central category while other categories, such as [[quantity]], [[Quality (philosophy)|quality]], and place, depend on substances or act as modifications.<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.1 Aristotelian Realism}} | {{harvnb|Studtmann|2024|loc=§ 2. The Ten-Fold Division}} | {{harvnb|Wardy|1998|loc=§ 1. Categories in Aristotle}} }}</ref> [[Immanuel Kant]] outlined [[Category (Kant)|a system of twelve categories]], which he regarded as pure concepts of understanding, divided into the classes of quantity, quality, relation, and modality.<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.2 Kantian Conceptualism}} | {{harvnb|Wardy|1998|loc=§ 1. Categories in Kant}} }}</ref> Other theories in the [[History of Western philosophy|Western tradition]] were proposed by [[Edmund Husserl]], [[Samuel Alexander]], [[Roderick Chisholm]], and [[E. J. Lowe (philosopher)|E. J. Lowe]].<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.3 Husserlian Descriptivism, § 1.4 Contemporary Category Systems}} | {{harvnb|Grim|Rescher|2023|loc=[https://books.google.com/books?id=KgPPEAAAQBAJ&pg=PT39 § Various Recents]}} }}</ref> In ancient [[Hindu philosophy]], the school of [[Samkhya]] identified [[Purusha|pure consciousness]] and [[Prakriti|matter]] as the two foundational principles of reality,<ref>{{multiref | {{harvnb|Robinson|Weir|2025|loc=§ 2.1 Dualism in Indian Philosophy}} | {{harvnb|Ruzsa|loc=Lead section, § 4d. Evolution, Humanity and the World}} | {{harvnb|Harzer|2005|p=8089}} }}</ref> while the school of [[Vaisheshika]] proposed a system of six categories: substance, quality, motion, universal, particular, and inherence.<ref>{{multiref | {{harvnb|Kumar|2019|pp=[https://books.google.com/books?id=Jr2YDwAAQBAJ&pg=PA34 34–36]}} | {{harvnb|Leaman|2002|p=269}} | {{harvnb|Westerhoff|2019|loc=§ Three important systems of categories: Vaiśeṣika}} }}</ref> In [[Ancient Chinese philosophy|ancient Chinese thought]], [[Taoism]] regarded the [[Tao]] as the omnipresent, self-existent, imperceptible, and incomprehensible source of all existence.<ref>{{multiref | {{harvnb|Yijie|2012|pp=[https://books.google.com/books?id=OtkMuSA5pNsC&pg=PA170 149–176]}} | {{harvnb|Dynes|2016|pp=[https://books.google.com/books?id=pxjOEAAAQBAJ&pg=PA60 60–61]}} }}</ref> The related yinyang school treated [[yin and yang]] as two correlated forces whose interaction underlies all natural processes.<ref>{{multiref | {{harvnb|Bianchi|2025|loc=§ China}} | {{harvnb|Wang|loc=Lead section, § 1. Origins of the Terms Yin and Yang}} }}</ref>

Physicists use concepts such as [[elementary particle]], [[force]], [[Field (physics)|field]], and [[spacetime]] to analyze the fundamental constituents of the universe. In [[quantum mechanics]], the [[Standard Model]] describes all known elementary particles, dividing them into two classes: [[fermions]], such as [[electrons]], and [[bosons]], such as [[photons]]. It also describes their interactions through all [[fundamental forces]] except [[gravity]], which is explained by the theory of [[general relativity]]. [[String theory]] is an attempt to unify quantum mechanics and general relativity, positing tiny vibrating strings as the basic constituents underlying elementary particles and their interactions.<ref>{{multiref | {{harvnb|Sebens|2020|loc=Lead section, § What Electrons Feel}} | {{harvnb|Krause|2014|pp=[https://books.google.com/books?id=wx63CgAAQBAJ&pg=PA227 227, 230–231, 234, 236]}} | {{harvnb|Perkowitz|2019|loc=§ 20th-century Surprises, § The Next Correlation, § Physics Subdivided, § A Radical Quantum Theory, § Strings and the Multiverse}} }}</ref>

== Structure ==
=== Composition ===
The structure of reality concerns the fundamental patterns of being, describing how entities are organized and interact with each other. [[Mereology]] is the theory of part–whole relations, examining how entities compose larger wholes and the laws governing their composition. Many everyday objects are complex entities made up of several parts. For example, a table is composed of a tabletop and the legs supporting it. Parts can themselves be made up of smaller parts, such as the [[molecules]] that constitute the tabletop.<ref>{{multiref | {{harvnb|Effingham|Beebee|Goff|2010|pp=121, 156}} | {{harvnb|Heil|2005|p=790}} | {{harvnb|Loux|Crisp|2017|pp=250–251}} | {{harvnb|Cornell|loc=Lead Section, § 2. The Special Composition Question}}}}</ref>

Various theories of the mereological principles underlying composition have been proposed. Mereological universalism holds that any collection of entities constitutes a whole, even if the entities are otherwise unrelated. According to mereological moderatism, groups of entities must meet certain conditions to count as a whole. One suggested condition is that the parts are in contact with each other, excluding arbitrary groupings, such as a collection made up of the [[Great Wall of China]] and [[Mexico City International Airport]]. [[Mereological nihilism|Mereological nihilists]] deny that any wholes exist, arguing that fundamentally, there are only simple entities and no composites.<ref>{{multiref | {{harvnb|Weatherson|2023|loc=Lead section, § 3. Overpopulation}} | {{harvnb|Loux|Crisp|2017|pp=82–83}} | {{harvnb|Cornell|loc=Lead Section, § 2. The Special Composition Question}} | {{harvnb|Brenner|2015|p=1295}} | {{harvnb|Tallant|2017|pp=19–21, 23–24, 32–33}} }}</ref> 

=== Fundamentality ===
[[File:Fundamental and non-fundamental.svg|thumb|alt=Diagram with the terms "fundamental", "non-fundamental", and an arrow|According to some proposals, reality has a hierarchical structure in which fundamental entities ground non-fundamental ones.<ref>{{multiref | {{harvnb|Tahko|2023|loc=§ Lead section}} | {{harvnb|McKenzie|2022|pp=[https://books.google.com/books?id=bMBgEAAAQBAJ&pg=PA1 1–2]}} | {{harvnb|Schaffer|2010|pp=31–32}} }}</ref>]]
Another structural feature concerns the idea that some entities depend on, or are grounded in, other entities. For example, one view suggests that macroscopic objects, such as a chair, depend on the microscopic objects that underlie them, such as elementary particles. Ontologists are particularly interested in the most fundamental level of reality, which is made up of entities that do not depend on anything else, are not grounded in other entities, or constitute a minimal basis that determines everything else.<ref>{{multiref | {{harvnb|Tahko|2023|loc=§ Lead section}} | {{harvnb|McKenzie|2022|pp=[https://books.google.com/books?id=bMBgEAAAQBAJ&pg=PA1 1–2]}} | {{harvnb|Schaffer|2010|pp=31–32}} }}</ref>

There are different ways to conceptualize the relation between fundamental and non-fundamental entities, including the ideas of [[Ontology#Other concepts|ontological dependence]], [[metaphysical grounding]], [[Reductionism|reduction]], [[supervenience]], and [[emergence]]. Some outlooks suggest that only the fundamental level is ultimately real, arguing that non-fundamental entities are in some sense eliminable since reality can be described without them. A different view contends that dependence does not entail eliminability. For example, strong emergence theories assert that higher-level entities are genuinely novel and causally interact with lower-level entities without being reducible to them.<ref>{{multiref | {{harvnb|Tahko|2023|loc=§ Lead section, § 1. Varieties of Fundamentality, § 3. Metaphysical Foundationalism}} | {{harvnb|Ioannidis|Vishne|Hemmo|Shenker|2022|pp=[https://books.google.com/books?id=TD90EAAAQBAJ&pg=PA1 1–3]}} | {{harvnb|Chalmers|2022|loc=§ What Is Reality?, Footnote 115}} | {{harvnb|Vintiadis|loc=§2.a.i. Strong and Weak Emergence}} }}</ref> Flat ontologies deny that there is a hierarchical structure to reality, claiming that all entities exist on the same level.<ref>{{harvnb|Schaffer|2009|pp=[https://books.google.com/books?id=I_1QEAAAQBAJ&pg=PA54 54–55]}}</ref>

[[Absolute (philosophy)|The Absolute]], a closely related concept, is conceived as an ultimate reality that is self-existent, free from external conditions, and independent of anything else. The concept is discussed in [[German idealism]] and in various [[Theology|theological]] traditions.<ref>{{multiref | {{harvnb|McInerny|2003|loc=Lead section, § Summary}} | {{harvnb|Sprigge|2005|p=2}} }}</ref> In the [[Hindu philosophy|Hindu tradition]], it is often identified with [[Brahman]] as the all-pervasive reality and the supreme principle grounding all being. For example, the school of [[Advaita Vedanta]] distinguishes the ultimate, divine reality of Brahman from the field of illusory appearances, termed ''[[Maya (religion)|Maya]]'', associated with the empirical realm of everyday experience.<ref>{{multiref | {{harvnb|Menon|loc=Lead section, § 2. Metaphysics and Philosophy}} | {{harvnb|Pani|1993|pp=[https://books.google.com/books?id=KMb9MmZTAdsC&pg=PA39 17–18, 38–39]}} }}</ref>

==== Levels of reality ====
Some philosophical approaches rely on the idea of fundamentality and dependence to analyze the world in terms of levels or layers, such as [[Matter|material]], [[Life|biological]], [[Mind|psychological]], and [[social reality]]. One perspective interprets these levels as a [[methodological]] tool or a way of organizing scientific research: [[physics]] studies matter, whereas [[biology]] investigates living [[organisms]], and [[psychology]] examines the mind. A more metaphysical outlook suggests that the different levels are not merely a methodological convenience but reflect the inherent structure of reality. On this view, higher levels show greater complexity and new phenomena but depend on the lower ones and could not exist without them. Lower levels, by contrast, operate according to more basic mechanisms and are prior to the higher ones. In this sense, there can be matter without biological life, whereas life is built upon matter and depends on it.<ref>{{multiref | {{harvnb|Heil|2005|p=790}} | {{harvnb|Ioannidis|Vishne|Hemmo|Shenker|2022|pp=[https://books.google.com/books?id=TD90EAAAQBAJ&pg=PA1 1–3]}} | {{harvnb|Peterson|Poli|2026|loc=§ 5.2 Strata}} }}</ref>

[[Non-reductive physicalism|Non-reductive physicalists]] hold that everything is ultimately physical while insisting that higher-level psychological facts cannot be reduced to fundamental physics. According to this view, even a complete understanding of physics would not render sciences dedicated to higher levels, such as psychology, obsolete. For example, one suggestion frames [[mental states]] as [[Functionalism (philosophy of mind)|psychological functions]] that are not limited to human brains or specific patterns of neural activation but can be realized by different physical substrates.<ref>{{multiref | {{harvnb|Ioannidis|Vishne|Hemmo|Shenker|2022|pp=[https://books.google.com/books?id=TD90EAAAQBAJ&pg=PA7 7–9]}} | {{harvnb|Heil|2004|pp=[https://books.google.com/books?id=xJ9TlR1pMhQC&pg=PA179 179, 188–189]}} | {{harvnb|Ben-Menahem|2022|pp=[https://books.google.com/books?id=TD90EAAAQBAJ&pg=PA15 15–17]}} }}</ref>

Similar discussions address the question of how or to what extent a shared social reality is grounded in the psychological activities of individuals. Social reality encompasses facts about [[institution]]s and [[Social norm|norms]], such as [[money]], [[law]], and [[language]]. According to one proposal, it is grounded in shared psychological attitudes as the members of a [[society]] collectively accept and act in accordance with these institutional rules and meanings, like when a piece of paper counts as money because of how people treat and use it.<ref>{{multiref | {{harvnb|Searle|1995|pp=[https://books.google.com/books?id=zrLQwJCcoOsC&pg=PR11 xi–xii, 1–2, 13, 23–24, 27–28]}} | {{harvnb|Koepsell|2016|pp=[https://books.google.com/books?id=_raiDQAAQBAJ&pg=PA79 79–82]}} }}</ref>

=== Monism and pluralism ===
[[File:Frans Hals - Portret van René Descartes.jpg|thumb|upright=.8|alt=Painting of a bearded man with long hair wearing a dark formal attire|According to [[René Descartes]]'s substance dualism, reality is made up of two kinds of entities: matter and mind.<ref>{{multiref | {{harvnb|Hamlyn|2005|p=591}} | {{harvnb|Dehsen|2013|p=[https://books.google.com/books?id=cU7cAAAAQBAJ&pg=PA51 51]}} }}</ref>]]
[[Monism]] and [[Pluralism (philosophy)|pluralism]] are families of views about the roles of unity and multiplicity in the structure of reality. Existence monism holds that reality is ultimately composed of only a single concrete entity: the whole [[world]] is a single object, and all the individual entities encountered in everyday life, such as trees and animals, are not independent objects but merely features of the world-object or ways in which it appears. Existence monism contrasts with existence pluralism, which aligns more closely with everyday experience by asserting that reality is made up of many objects.<ref>{{multiref | {{harvnb|Schaffer|2018|loc=Lead section, § 1.1 Many Monisms}} | {{harvnb|Meyer|2025|loc=§ 4.1 Modes and Existence Monism}} }}</ref>

Another debate on the monism-pluralism spectrum concerns not the number of entities but the kinds to which these entities belong.<ref>{{harvnb|Schaffer|2018|loc=Lead section, § 1.1 Many Monisms}}</ref> [[Mind–body dualism]] is a form of pluralism asserting that mind and body are two fundamentally different kinds that make up reality.<ref>{{multiref | {{harvnb|Schaffer|2018|loc=§ 1.1 Many Monisms}} | {{harvnb|Nagel|2005|p=221}} | {{harvnb|Robinson|Weir|2025|loc=§ 1. Dualism and the Mind-Body Problem}} }}</ref>{{efn|[[Substance dualism|Substance dualists]] maintain that mind and body are distinct substances, while [[Property dualism|property dualists]] regard them as different properties of the same substance.<ref>{{multiref | {{harvnb|Robinson|Weir|2025|loc=§ 3.1 Substance Dualism, § 3.2 Property Dualism}} | {{harvnb|Lowe|2009|pp=66–68}} }}</ref>}} Monist views, by contrast, hold that everything belongs to the same kind. [[Metaphysical idealism|Idealist monism]] maintains that reality is essentially mental, whereas [[neutral monism]] proposes that reality is fundamentally neither physical nor mental but neutral.<ref>{{multiref | {{harvnb|Jaworski|2011|pp=5, 246, 256}} | {{harvnb|Searle|2004|pp=44, 47–48}} }}</ref> The dominant approach since the 20th century has been [[Physicalism|physicalist monism]], which holds that everything is physical. Different versions of physicalism provide distinct accounts of the place and role of the mind in a purely physical reality. [[Eliminative materialism|Eliminative physicalism]] denies the existence of mental entities, while [[Reductive physicalism|reductive]] and non-reductive physicalism explain them in terms of physical processes. For example, [[behaviorism]] reduces mental concepts to observable behavior, and functionalism suggests a non-reductive account that identifies mental concepts with functional roles realizable by different systems.<ref>{{multiref | {{harvnb|Jaworski|2011|pp=68, 71–73, 102–104}} | {{harvnb|Searle|2004|pp=48–52, 62}} | {{harvnb|Kind|2020|loc=§ 3. Physicalism}} }}</ref>

=== Spacetime and laws of nature ===
[[Space]] and [[time]] are frameworks that structure reality by organizing how entities relate to one another. A classical understanding conceives them as distinct frameworks: space as a [[Three-dimensional space|three-dimensional]] continuum in which entities are located, and time as a one-dimensional progression from the past, through the present, and into the future. In [[modern physics]], [[general relativity]] regards them as a unified framework in which spatial and temporal dimensions are interwoven and measurements of space and time are influenced by the observer's motion.<ref>{{multiref | {{harvnb|Dowden|loc=§ 3.a. History of Answers}} | {{harvnb|Weinert|2004|pp=[https://books.google.com/books?id=-R4ANHu-csMC&pg=PA130 130–131]}} | {{harvnb|Clifton|2005|p=887}} }}</ref> In philosophy, realists and idealists debate whether space and time exist independently of the human mind or are cognitive constructs that organize sensory experience.<ref>{{multiref | {{harvnb|Dainton|2010|pp=245–246}} | {{harvnb|Janiak|2022|loc=§ 4.2 Absolute/Relational Vs. Real/Ideal}} | {{harvnb|Pelczar|2015|p=[https://books.google.com/books?id=tkjTBgAAQBAJ&pg=PA115 115]}} }}</ref>{{efn|For example, [[Immanuel Kant]] held that space and time are subjective forms through which the mind organizes appearances. [[J. M. E. McTaggart]] argued that the concept of time involves contradictory elements and concluded that [[The Unreality of Time|time is an illusion]].<ref>{{multiref | {{harvnb|Guyer|1998|loc=§ 5. Space, Time and Transcendental Idealism)}} | {{harvnb|Dainton|2010|pp=13–17, 219}} }}</ref>}} Absolutists and [[Relationalism#Relationalism (theory of space and time)|relationalists]] discuss whether [[spacetime]] is itself a distinct object, such as a huge container, or a network of relations between objects.<ref>{{multiref | {{harvnb|Hoefer|Huggett|Read|2023|loc=Lead Section}} | {{harvnb|Benovsky|2016|pp=[https://books.google.com/books?id=4KHWCwAAQBAJ&pg=PA19 19–20]}} | {{harvnb|Romero|2018|p=[https://books.google.com/books?id=5wJ2DwAAQBAJ&pg=PA135 135]}} }}</ref> [[Eternalism (philosophy of time)|Eternalism]] is the view that past, present, and future are equally real. It contrasts with the [[growing block universe]] theory, which claims that the future is not real, and with [[Philosophical presentism|presentism]], which holds that only the present is real.<ref>{{harvnb|Merricks|2006|p=[https://books.google.com/books?id=cqOM0YJuzXEC&pg=PA103 103]}}</ref>

The concept of [[causality]] describes relations between entities in spacetime. It links causes and effects as entities interact and influence each other, as when a thrown rock is the cause and a shattered window the effect.<ref>{{multiref | {{harvnb|Carroll|Markosian|2010|pp=20–22}} | {{harvnb|Tallant|2017|pp=218–219}} }}</ref> Causality is closely related to [[disposition]]s or powers, which are capacities of entities to change or bring about changes in other entities, such as [[flammability]] or [[electrical conductivity]].<ref>{{harvnb|Choi|Fara|2021|loc=Lead, § 1. Analyses of Disposition Ascriptions}}</ref>

[[Scientific law|Laws of nature]] are uniformities or regularities in the structure of reality: they describe patterns of how entities interact and how changes unfold. For example, the [[laws of thermodynamics]] describe how [[heat]] and other forms of [[energy]] behave, such as the idea that [[Conservation of energy|the total amount of energy is always conserved]]. Laws of nature play a central role in the physical sciences by providing frameworks for predicting outcomes under specified conditions.<ref>{{multiref | {{harvnb|Swartz|loc=Lead section}} | {{harvnb|Hoefer|2026|loc=§ 2.4 Laws of Nature}} | {{harvnb|Kreith|West|1996|pp=[https://books.google.com/books?id=PePq7o6mAbwC&pg=PA19 19–21]}} }}</ref>

[[Causal determinism]] is the view that every event is fully determined or necessitated by prior events. According to this view, what happened in the past fixes what will happen in the future, including [[human behavior]]. It is controversial whether determinism is true and, if so, whether this implies that there is no [[free will]]. Some [[Interpretations of quantum mechanics|interpretations of quantum mechanics]] hold that measurement outcomes are inherently probabilistic, thereby rejecting causal determinism, but this is not true for all interpretations.<ref>{{multiref | {{harvnb|Hoefer|2026|loc=Lead section, § 1. Introduction, § 2.5 Fixed, § 4.4 Quantum Mechanics}} | {{harvnb|Armstrong|2018|pp=[https://books.google.com/books?id=uf7EDwAAQBAJ&pg=PA93 93–94]}} }}</ref>{{efn|[[Causal closure]], a related idea, is a proposed principle stating that every physical event has a sufficient physical cause. It implies that no non-physical entities can have physical effects.<ref>{{harvnb|Ben-Menahem|2022|pp=[https://books.google.com/books?id=TD90EAAAQBAJ&pg=PA11 11, 13, 20–21]}}</ref>}}

[[Cosmological models]] describe the large-scale structure and dynamics of the universe. The widely accepted [[Big Bang]] theory holds that the universe began about 13.8 billion years ago, initially in an extremely hot, dense state, expanding and cooling ever since. Proposals for the [[Ultimate fate of the universe|long-term future of the universe]] vary. Some predict that the expansion will continue indefinitely. Others maintain that the expansion will eventually stop and reverse, resulting in a [[Big Crunch]]. [[Cyclic model|Cyclic theories]] posit an endless sequence of expansions and contractions, with each Big Crunch leading to a new Big Bang.<ref>{{multiref | {{harvnb|Steinhardt|2014|loc=§ 2. The Cyclic Universe}} | {{harvnb|Hooft|Vandoren|2014|pp=[https://books.google.com/books?id=hy-7CgAAQBAJ&pg=PA83 83–84]}} | {{harvnb|Börner|2004|pp=[https://books.google.com/books?id=cDJw3dWjw_UC&pg=PA3 3–4]}} }}</ref>

== Realism and anti-realism ==
[[Philosophical realism|Realism]] and anti-realism are families of views concerning the mind-independence of reality. In the broadest sense, realism is the view that the external world and its constituents exist as they do regardless of how people perceive or think about them. In this sense, reality does not depend on human knowledge or [[consciousness]] and exists apart from them, including the aspects that no one is aware of.<ref>{{multiref | {{harvnb|Hirst|2006|loc=Lead section, § The Polemic against Idealism}} | {{harvnb|Marshall|2005}} | {{harvnb|Miller|2026|loc=Lead section, § 1. Preliminaries}} | {{harvnb|Craig|1998a|loc=Lead section}} }}</ref>

Anti-realism rejects this view, arguing instead that there is no external world or that reality depends in certain respects on mental processes, subjective perspectives, or social conventions. For example, [[metaphysical idealism]] asserts that everything is essentially mental, for instance, by understanding material objects as ideas in the mind. [[Phenomenalism]], a related view, reduces physical objects to collections of actual or possible sensory experiences.<ref>{{multiref | {{harvnb|Hirst|2006|loc=Lead section, § The Polemic against Idealism}} | {{harvnb|Miller|2026|loc=Lead section}} }}</ref> [[Relativism]], another form of anti-realism, holds that what counts as real varies based on one's perspective or [[conceptual framework]]. [[Social constructionism|Constructivism]] asserts that reality is constructed rather than discovered.<ref>{{multiref | {{harvnb|Craig|1998|loc=Lead section, § 1. Grades of Relativism, § 2. The Credibility of Relativism}} | {{harvnb|Goswick|loc=Lead section, § 1. What Is Constructivism?}} }}</ref> Quietism takes a different approach by seeking to undermine the discussion between realism and anti-realism. It holds that the debate is not based on a substantive disagreement but arises instead from conceptual confusions.<ref>{{harvnb|Miller|2026|loc=§ 8. Views which Undermine the Debate: Quietism}}</ref>

Disputes between realism and anti-realism often focus on specific types of entities rather than reality as a whole, including discussions about whether [[universals]], [[abstract objects]], and [[values]] have mind-independent existence. In this sense, realism and anti-realism encompass many domain-specific positions across diverse fields. For example, a person may be a realist about universals and an anti-realist about values.<ref>{{multiref | {{harvnb|Miller|2026|loc=Lead section}} | {{harvnb|Craig|1998a|loc=Lead section}} }}</ref>

=== Universals ===
{{multiple image
|perrow            = 2
|total_width       = 350
|image1            = Color yellow.svg
|alt1              = Patch of yellow
|image2            = FullMoon2010.jpg
|alt2              = Photo of the Moon
|footer            = Realists and anti-realists debate whether universals, such as the color [[yellow]], exist in addition to particulars, such as the [[Moon]].<ref>{{multiref | {{harvnb|MacLeod|Rubenstein|loc=Lead Section, § 2. Versions of Realism, § 3. Versions of Anti-Realism}} | {{harvnb|Bigelow|1998a|loc=§ 4. Nominalism and Realism}} | {{harvnb|Loux|Crisp|2017|pp=17–19, 45–46}} }}</ref>}}
Realism about universals affirms the mind-independent existence of universal or general entities, such as the color ''yellow''. [[Platonism]] about universals holds that they are part of reality in their own right, independent of the particular entities that instantiate them. This view maintains that there are not only individual yellow objects, such as bananas and sunflowers, but also the universal ''yellow'' itself, which, according to [[Plato]], exists in a [[Theory of Forms|separate non-spatiotemporal realm of Forms]]. [[Moderate realism]] agrees that universals have mind-independent reality but denies their existence in a separate realm. Instead, it affirms that universals exist in their instances, meaning that there would be no universal ''yellow'' without any yellow objects to instantiate it.<ref>{{multiref | {{harvnb|MacLeod|Rubenstein|loc=Lead Section, § 2. Versions of Realism}} | {{harvnb|Bigelow|1998a|loc=§ 4. Nominalism and Realism}} | {{harvnb|Loux|Crisp|2017|pp=17–19}} | {{harvnb|Hale|2020|loc=§ Universals}}}}</ref>

Anti-realism about universals denies their mind-independent existence. According to [[conceptualism]], universals exist in the mind as concepts through which people categorize and order their impressions, acting as tools of cognitive organization rather than properties of external entities. [[Nominalism]], another anti-realist view, rejects both mental and non-mental interpretations of universals. It argues that there are only [[particulars]], for example, by explaining apparent universals through words used to group entities or through resemblance among particulars.<ref>{{multiref | {{harvnb|MacLeod|Rubenstein|loc=Lead Section, § 3. Versions of Anti-Realism}} | {{harvnb|Bigelow|1998a|loc=§ 4. Nominalism and Realism}} | {{harvnb|Loux|Crisp|2017|pp=17–19, 45–46}} }}</ref>

=== Abstract objects ===
[[File:Number 7.svg|thumb|alt=Number 7|upright=.6|In the philosophy of mathematics, realism and anti-realism discuss whether mathematical objects, such as the number [[7]], have mind-independent reality.<ref>{{multiref | {{harvnb|Balaguer|2009|pp=[https://books.google.com/books?id=mbn35b2ghgkC&pg=PA35 35–38, 44–46]}} | {{harvnb|Irvine|2009|p=[https://books.google.com/books?id=mbn35b2ghgkC&pg=PR11 xi]}} }}</ref>]]
Realists and anti-realists about abstract objects debate whether, or in what sense, such entities form part of reality. According to realism, abstract objects, such as [[number]]s, [[Set (mathematics)|sets]], and [[mathematical functions]], exist in their own right, in addition to concrete objects, such as flowers and cars. Realists often argue that everyday discourse and scientific language frequently refer to apparent abstract entities, suggesting that their existence is already assumed by these practices.{{efn|This idea is central to [[Quine–Putnam indispensability argument|indispensability arguments]], which affirm the existence of abstract objects based on the claim that such entities are indispensable scientific explanations.<ref>{{harvnb|Colyvan|2001|pp=[https://books.google.com/books?id=bns8DwAAQBAJ&pg=PA6 6–10]}}</ref>}} An influential challenge comes from their purported existence outside space, time, and causality, raising the question of how humans as concrete beings could know about such entities.<ref>{{multiref | {{harvnb|Plebani|2020|pp=[https://books.google.com/books?id=2pbiDwAAQBAJ&pg=PA1 1–5]}} | {{harvnb|Falguera|Martínez-Vidal|2020|pp=[https://books.google.com/books?id=2pbiDwAAQBAJ&pg=PR6 vi–viii, ix]}} | {{harvnb|Tallant|2017|pp=48–56}} }}</ref>

Anti-realists hold that there are no abstract objects and offer alternative explanations. [[Fictionalism|Fictionalists]] argue that discourse about abstract objects concerns fictional entities within make-believe frameworks. It holds that this practice can be useful in some contexts without ascribing substantive or framework-independent reality to such entities. Another approach is to [[paraphrase]] sentences that seem to refer to abstract objects. This method seeks to show that apparent commitments to abstract objects can be eliminated and that the claims in question are ultimately only about concrete entities.<ref>{{multiref | {{harvnb|Falguera|Martínez-Vidal|2020|pp=[https://books.google.com/books?id=2pbiDwAAQBAJ&pg=PR8 viii–ix]}} | {{harvnb|Tallant|2017|pp=56–59, 69–73}} }}</ref>

The problem of abstract objects is central to the [[philosophy of mathematics]] and the question of whether mathematical statements are about genuinely existing entities. [[Mathematical Platonism]] is a form of realism arguing that mathematical objects, like numbers, have mind-independent existence outside space and time. Anti-realism about abstract objects in mathematics takes various forms, including, but not limited to, fictionalism. For example, [[psychologism]] asserts that mathematical objects are mental constructions or ideas rather than abstract objects. According to [[conventionalism]], the truth of mathematical statements rests on linguistic conventions or definitions, rather than on their relation to language-independent reality. [[Formalism (philosophy of mathematics)|Formalism]], another form of anti-realism, understands mathematics as a practice of [[symbol]] manipulation, suggesting that [[mathematical truth]] is grounded in whether the manipulation rules permit the construction of a [[Proof (mathematics)|proof]].<ref>{{multiref | {{harvnb|Balaguer|2009|pp=[https://books.google.com/books?id=mbn35b2ghgkC&pg=PA35 35–38, 44–46]}} | {{harvnb|Irvine|2009|p=[https://books.google.com/books?id=mbn35b2ghgkC&pg=PR11 xi]}} }}</ref>

=== Values ===
[[Value theory#Realism and anti-realism|Axiological realism and anti-realism]] discuss the ontological status of values. Some positions concern the existence of values in general, while others are limited to specific domains, such as [[Morality|moral]], [[aesthetic]], or [[religious]] values.<ref>{{multiref | {{harvnb|Harold|2023|pp=[https://books.google.com/books?id=ZCnPEAAAQBAJ&pg=PA6 1–14]}} | {{harvnb|Rescher|1969|pp=15–16}} | {{harvnb|Zagzebski|2004|p=[https://books.google.com/books?id=KhqPito92b8C&pg=PA11 11]}} | {{harvnb|Oddie|2013|loc=Lead section}} }}</ref>

Realists hold that values are objective features of reality, meaning that there are mind-independent facts about whether something is [[good]] or bad, irrespective of subjective beliefs or personal preferences.<ref>{{multiref | {{harvnb|Zagzebski|2004|p=[https://books.google.com/books?id=KhqPito92b8C&pg=PA11 11]}} | {{harvnb|Oddie|2013|loc=Lead section}} }}</ref> [[Ethical naturalism|Naturalism]] argues that values are part of the natural world and can be studied by the natural sciences through empirical observation. [[Ethical non-naturalism|Non-naturalism]], another form of realism, maintains that values differ significantly from empirical properties and belong to another domain of reality.<ref>{{multiref | {{harvnb|Frankena|2006|pp=639–640}} | {{harvnb|DeLapp|loc=§ 4a. Moral Realisms}} | {{harvnb|FitzPatrick|2011|pp=7–8}} }}</ref> 

Anti-realist views reject the mind-independent existence of values and can take various forms. According to [[subjectivism]], values depend on the attitudes and preferences of individuals. For example, [[emotivism]] holds that value statements express emotional attitudes of subjective approval or disapproval rather than objective facts. [[Error theory]] asserts that all value statements are false because there are no values. Another form of anti-realism maintains that value statements are neither true nor false but meaningless.<ref>{{multiref | {{harvnb|Oddie|2013|loc=Lead section, § Are Value Claims Truth Evaluable?,  § Do Value Claims Have Truth Makers?, § Value Realism by Degrees: a Flow Chart}} | {{harvnb|Oliver|1998}} | {{harvnb|Rønnow-Rasmussen|2015|p=[https://books.google.com/books?id=uvzVBgAAQBAJ&pg=PA34 34]}} }}</ref>

=== Science ===
[[Scientific realism]] is the view that the best [[scientific theories]] provide an accurate description of a mind-independent world. It holds that the scientific view of the world is either exactly or at least approximately true by presenting reality as it is. This position is particularly relevant to the status of [[unobservable]] objects{{em dash}}entities that cannot be directly perceived but are nonetheless posited by scientific theories to explain observable phenomena. For example, dogs and chairs are observable since they can be directly perceived by [[Sense|human sensory organs]] under the right conditions, whereas electrons and [[wave function]]s are unobservable and inferred from indirect evidence. Accordingly, scientific realists argue that the unobservable entities posited by the best scientific theories are not mere fictions but correspond to genuine features of reality.<ref>{{multiref | {{harvnb|Chakravartty|Massimi|Sprevak|2025|loc=Lead section, § 1. What is Scientific Realism?}} | {{harvnb|Liston|loc=Lead section, § 5. Scientific Realism}} }}</ref>

[[Structural realism]] is an influential version of scientific realism that modifies how the reality of unobservable entities is understood. It holds that scientific theories are only approximately true: they correctly describe the underlying relational structure of reality but may contain inaccuracies about the unobservable entities they posit.<ref>{{multiref | {{harvnb|Ladyman|2023|loc=Lead section, § 1. Introduction}} | {{harvnb|Liston|loc=§ 11.a. Structuralism}} }}</ref>{{efn|A key motivation for this approach is the observation that the descriptions of unobservable entities in past scientific theories have often been revised to accommodate new empirical findings, although they correctly predicted more general structural features of reality.<ref>{{harvnb|Ladyman|2023|loc=Lead section, § 1. Introduction, § 2. The Best of Both Worlds?}}</ref>}}

Anti-realism questions the prospect of achieving a true description of a mind-independent world. For example, [[instrumentalism]] asserts that scientific theories are tools for making accurate predictions. On this view, unobservable entities may be invoked in theory construction to aid prediction but should not be taken to exist. [[Constructive empiricism]], a closely related view, holds that scientific theories aim at empirical adequacy rather than full truth and may employ theoretical posits as long as they produce accurate descriptions of observable phenomena.<ref>{{multiref | {{harvnb|Liston|loc=§ 6. Constructive Empiricism, § 11.b. Stanford's New Induction}} | {{harvnb|Fine|1998|loc=Lead section}} | {{harvnb|Dent|2005|p=436}} }}</ref>

In physics, [[local realism]] is a view that combines the [[principle of locality]] with the notion that reality exist and have definite properties, whether or not they are being observed by someone.<ref>{{Cite journal |last=Lambare |first=Justo Pastor |date=2022-09-05 |title=On the Meaning of Local Realism |url=https://doi.org/10.1007/s10701-022-00618-1 |journal=Foundations of Physics |language=en |volume=52 |issue=5 |pages=98 |doi=10.1007/s10701-022-00618-1 |issn=1572-9516}}</ref> The principle of locality is the idea that physical objects are influenced only by their immediate surroundings: there is no direct or instantaneous [[action at a distance]]; all interactions occur and propagate through local mechanisms. Empirical evidence has ruled out the combination of locality and realism, concluding that observations are either influenced by [[Quantum nonlocality|non-local]] factors or depend on the act of measurement.<ref>{{multiref | {{harvnb|Laudisa|2023|pp=Abstract, § Introduction}} | {{harvnb|BESIII Collaboration|2025|loc=§ Introduction}} }}</ref>

In the [[social sciences]], [[Critical realism (philosophy of the social sciences)|critical realism]] holds that observable events in the social world only partially disclose reality. It asserts that they are the manifestations of unobservable but manipulable mechanisms, which are considered equally real.<ref>{{multiref | {{harvnb|Zhang|2023|loc=§ 1. Introduction}} | {{harvnb|Mukumbang|De Souza|Eastwood|2023|loc=§ Critical Realism}} }}</ref>

=== Others ===
[[Modal realism]] is the view that possible worlds are as real as the actual world. On this view, reality is made up of countless concrete worlds existing in parallel without interacting with one another. The only thing distinguishing the actual world from other possible worlds is the observer's standpoint: the actual world is the observer's own world, while other possible worlds are inhabited by [[Counterpart theory|counterparts]].<ref>{{multiref | {{harvnb|Menzel|2016|loc=§ 2. Three Philosophical Conceptions of Possible Worlds}} | {{harvnb|Parent|loc=Lead section, § 2. Lewis' Realism}} }}</ref>

[[Speculative realism]] is a form of realism in [[continental philosophy]]. It opposes the idea that world and mind are essentially correlated, emphasizing the mind-independent nature of reality beyond the way humans perceive and think about it.<ref>{{harvnb|Harman|2018|loc=§ Introduction}}</ref>

A [[semantic]] approach to the debate between realism and anti-realism, proposed by [[Michael Dummett]], argues that the underlying disagreement concerns the meaning of statements rather than the existence of entities. It characterizes realism as the view that the truth or meaning of sentences is determined by external standards or mind-independent reality. [[Anti-realism]] is understood as a view that identifies the meaning of a statement with the [[evidence]] that would support it or the conditions under which a person is [[Justification (epistemology)|justified]] in asserting it. Dummett concludes that, according to realism, [[Principle of bivalence|a sentence is either true or false]], while according to anti-realism, there is [[Three-valued logic|a third option]] for undecidable sentences that can be neither verified nor falsified.<ref>{{multiref | {{harvnb|Loux|2005|pp=633–637}} | {{harvnb|Craig|1998a|loc=Lead section, § 4. Logical and Semantic Versions}} | {{harvnb|Miller|2026|loc=Lead section, § 6. Views Opposing the Independence Dimension (I): Semantic Realism}} }}</ref>

== Knowledge ==
[[Knowledge]] is an awareness or familiarity that shapes how individuals understand and engage with reality. It is a successful cognitive contact with reality, often associated with [[Truth|an accurate grasp of how things are]] and with having good reasons or [[Justification (epistemology)|justification]] for one's perspective.<ref>{{multiref | {{harvnb|Zagzebski|1999|p=109}} | {{harvnb|Steup|Neta|2024|loc=Lead section, § 1. The Varieties of Cognitive Success}} | {{harvnb|Crumley II|2009|pp=53–54}}}}</ref> 

Philosophers discuss various sources of knowledge as ways of how this cognitive contact is established, including [[perception]], [[introspection]], [[reason]], [[memory]], and [[testimony]].<ref>{{multiref | {{harvnb|Kern|2017|pp=[https://books.google.com/books?id=eyh5DQAAQBAJ&pg=PA8 8–10, 133]}} | {{harvnb|Smith|2023|p=3}} | {{harvnb|Steup|Neta|2024|loc=§ 5. Sources of Knowledge and Justification}} | {{harvnb|Hetherington|loc=§ 3. Ways of Knowing}}}}</ref> Perception relies on [[Sense|sensory organs]] to acquire empirical information about the world, including [[Visual perception|vision]] and [[hearing]].<ref>{{multiref | {{harvnb|Steup|Neta|2024|loc=§ 5.1 Perception}} | {{harvnb|Hetherington|loc=§ 3. Ways of Knowing}} }}</ref> Introspection is an internal awareness of one's own [[mental states]].<ref>{{harvnb|Steup|Neta|2024|loc=§ 5.2 Introspection}}</ref> Reason is the ability to draw [[Logical reasoning|logical inferences]] and arrive at truths independent of immediate sensory input.<ref>{{multiref | {{harvnb|Hetherington|loc=§ 3d. Knowing by Thinking-Plus-Observing}} | {{harvnb|Steup|Neta|2024|loc=§ 5.4 Reason}} | {{harvnb|Audi|2002|pp=85, 90–91}} | {{harvnb|Audi|2006|p=[https://books.google.com/books?id=-YPTEeIhOXYC&pg=PA38 38]}} }}</ref> Memory is the capacity to store information from other sources and make it available to cognitive processes when needed.<ref>{{multiref | {{harvnb|Steup|Neta|2024|loc=§ 5.3 Memory}} | {{harvnb|Audi|2002|pp=72–75}} | {{harvnb|Gardiner|2001|pp=1351–1352}} }}</ref> Testimony is a transmission of knowledge from one person to another through [[communication]].<ref>{{harvnb|Steup|Neta|2024|loc=§ 5.5 Testimony}}</ref>{{efn|Testimony plays a central role in [[social epistemology]], which investigates how social processes shape the acquisition, transmission, and evaluation of knowledge within groups.<ref>{{multiref | {{harvnb|Tanesini|2017|loc=Lead section}} | {{harvnb|O'Connor|Goldberg|Goldman|2024|loc=Lead section, § 1. What Is Social Epistemology?, § 3.1 Testimony}} }}</ref>}}

The [[scientific method]] is a rigorous approach to arrive at scientific knowledge. It involves the formulation of a [[hypothesis]] to explain a phenomenon and then testing it with empirical evidence from [[controlled experiments]] or [[observation]]. A central aspect is [[replicability]]: procedures should be documented so that other researchers can reproduce the investigation to verify or refute the original findings.<ref>{{multiref | {{harvnb|Dodd|Zambetti|Deneve|2023|pp=[https://books.google.com/books?id=jXqAEAAAQBAJ&pg=PA11 11–12]}} | {{harvnb|Hatfield|1998}} | {{harvnb|Hepburn|Andersen|2021|loc=Lead Section, § 6.1 "The scientific method" in science education and as seen by scientists}} | {{harvnb|Moser|2005|p=390}}}}</ref>

[[Direct and indirect realism]] are different ways of understanding the relation between the objects in perceptual experience and the physical objects causing them. According to direct realism, there is no essential difference: the experienced objects are the real objects, implying a direct connection between perception and reality. A challenge for direct realism comes from [[Argument from illusion|erroneous perceptions]], such as [[illusions]], in which experienced entities do not correspond to real ones. Indirect realism seeks to resolve this problem by distinguishing between the mental entities involved in perception and the physical entities that cause them. On this view, the connection is indirect: entities such as [[ideas]] or [[sense data]] exist as part of experience and represent or point to mind-independent objects. Indirect realism faces the challenge of explaining how a true contact with reality is possible if people only perceive an internal veil of ideas or sense data, which stands between the subject and external reality.<ref>{{multiref | {{harvnb|O'Brien|loc=Lead section, § 1. Direct Realism; § 2. Indirect Realism}} | {{harvnb|Brown|1992|p=341}} | {{harvnb|Crumley II|2009|pp=268–269, 277–278, 300–301}} }}</ref>

=== Limits and objectivity ===
Philosophers examine various limitations of knowledge or obstacles to the cognitive contact with reality. Some are situation-specific, involving information that is inaccessible. For example, certain facts about the past may be unknowable today because they left no traces, such as facts about what [[Caesar]] had for breakfast on [[Assassination of Julius Caesar|the day he was assassinated]]. More general constraints arise from limits of human cognitive faculties rather than situation-specific circumstances, such as facts too complex for anyone to conceive.<ref>{{multiref | {{harvnb|Rescher|2009|pp=ix, 1–2, 6, 10, 93}} | {{harvnb|Rescher|2009a|pp=x–xi, 57–58, 140–141}} | {{harvnb|Markie|Folescu|2023|loc=§ 1. Introduction}} }}</ref> These limitations indicate a gap whereby reality is not fully captured and exceeds knowledge.<ref>{{harvnb|Rescher|2010|pp=20–24, 26–28, 50–53}}</ref>

Another issue concerns the possibility of [[Subjectivity and objectivity (philosophy)|objectivity]]. For example, judgments based on measurements are typically considered objective, such as the claim that the temperature is 20°C, whereas evaluative personal assessments are often regarded as subjective, such as the claims that this temperature is chilly or pleasant. One approach, first formulated by [[John Locke]], distinguishes between [[Primary–secondary quality distinction|objective primary qualities and subjective secondary qualities]]. According to this view, primary qualities, like size and shape, are real features of objects themselves, while secondary qualities, like colors and smells, are experiences caused by primary features but exist only in the perceiver's mind. A different approach, inspired by [[Kantian philosophy]], holds that all experienced phenomena are shaped by the innate structures of human cognition and cannot grasp the objective nature of the things in themselves. Defenders of objective knowledge often point to areas where there is broad intersubjective agreement among observers.<ref>{{multiref | {{harvnb|Mulder|loc=Lead section, § 2. Epistemological Issues}} | {{harvnb|Bunge|2006|pp=31, 42}} | {{harvnb|Brinkmann|2010|pp=[https://books.google.com/books?id=vuT31alSlQwC&pg=PA41 41–45]}} }}</ref> Some interpretations of quantum mechanics question the objectivity of measurements on the microscopic scale. They assert that observations of quantum phenomena are influenced by measurement processes, challenging the idea of observer-independent knowledge.<ref>{{multiref | {{harvnb|Heelan|2012|pp=[https://books.google.com/books?id=1UrvCAAAQBAJ&pg=PR11 xi–xii]}} | {{harvnb|Chalmers|McQueen|2022|pp=[https://books.google.com/books?id=gJ6FEAAAQBAJ&pg=PA11 11–14]}} }}</ref>

==== Skepticism ====
[[File:Braininvat.svg|thumb|alt=Diagram showing a brain connected to a computer|The [[brain in a vat|brain-in-a-vat]] thought experiment considers the possibility that all experiences are artificially generated through electrical brain stimulation, challenging the idea that people can know reality.<ref>{{multiref | {{harvnb|Putnam|1999|pp=30–31}} | {{harvnb|Crumley II|2009|pp=17}} }}</ref>]]
[[Skepticism]] is a family of views that question the possibility of knowledge. Some forms target specific domains of knowledge, such as [[religious skepticism]], which denies that beliefs about God or other religious doctrines amount to knowledge. [[Moral skepticism]] is the view that there is no moral knowledge, for instance, that one cannot know whether a given behavior is morally right or wrong. [[Metaphysics#Criticism|Skepticism about metaphysics]] holds that it is not possible to know the fundamental nature of reality, such as claims about [[categories of being]] or the existence of [[universals]].<ref>{{multiref | {{harvnb|Cohen|1998|loc=§ Article Summary}} | {{harvnb|Hookway|2005|p=838}} | {{harvnb|Moser|2011|p=[https://books.google.com/books?id=1ETRCwAAQBAJ&pg=PA200 200]}}}}</ref>

[[Radical skepticism|Radical]] or global skepticism is the most far-reaching form of skepticism. It denies the existence of knowledge in any form or domain, arguing that knowledge is impossible.<ref>{{multiref | {{harvnb|Hookway|2005|p=838}} | {{harvnb|Bergmann|2021|p=57}} | {{harvnb|Moreland|Craig|2003|p=[https://books.google.com/books?id=mPEN_EDiZuQC&pg=PA95 95]}} }}</ref> Although it is not a widely accepted position, various [[thought experiments]] undermining the reliability of human cognitive faculties are discussed in the academic literature. The [[dream argument]] asserts that a person can never be fully certain they are not currently [[dream]]ing, casting general doubt on the ability to distinguish reality from illusion at any moment. Similar ideas are explored in [[brain in a vat|brain-in-a-vat]] scenarios, which consider the possibility that all experiences are artificially generated through electrical brain stimulation, and in the [[evil demon]] thought experiment, which imagines a god-like being able to intrude on a person's inner life to deceive them at every turn.<ref>{{multiref | {{harvnb|Crumley II|2009|pp=17, 53–54}} | {{harvnb|Klein|1998|loc=§ 8. The Epistemic Principles and Scepticism}} | {{harvnb|Putnam|1999|pp=30–31}} }}</ref>

=== Augmented and virtual reality ===
While some skeptical scenarios use the idea of a simulated reality to challenge the reliability of human cognition, contemporary technologies such as [[augmented reality]] and [[virtual reality]] can also inform experience. Augmented reality encompasses devices that overlay digital information onto the physical world in real time. For example, it can take the form of wearable glasses that project navigational cues or contextual information into the field of vision. Virtual reality is further removed from the physical environment, immersing the user in a simulated setting, such as a [[video game]] world or a [[training simulation]].<ref>{{multiref | {{harvnb|Khan|Raouf|Cheng|2011|pp=[https://books.google.com/books?id=cAEKKXHTOVkC&pg=PA1 1–4]}} | {{harvnb|Ghaffar|Mullett|Pei|Roberts|2022|pp=[https://books.google.com/books?id=YN5mEAAAQBAJ&pg=PA14 14–17]}} }}</ref>

[[File:Virtuality continuum 2-en.svg|thumb|upright=1.6|alt=Diagram of the reality-virtuality continuum|Reality–virtuality continuum]]

The [[reality–virtuality continuum]] is a theoretical framework that posits a continuous scale of mixed reality forms. For example, augmented reality devices may provide only sparse cues or overlay dense layers of digital content. Similarly, virtual reality worlds may incorporate real-world objects into the simulation or be entirely virtual.<ref>{{multiref | {{harvnb|Khan|Raouf|Cheng|2011|pp=[https://books.google.com/books?id=cAEKKXHTOVkC&pg=PA1 1–4]}} | {{harvnb|Ghaffar|Mullett|Pei|Roberts|2022|pp=[https://books.google.com/books?id=YN5mEAAAQBAJ&pg=PA14 14–17]}} }}</ref>{{efn|In [[post-modern philosophy]], the term ''[[hyperreality]]'', coined by [[Jean Baudrillard]],  describes situations in which the distinction between reality and its representations breaks down, for example, because imitations acquire more legitimacy than the originals.<ref>{{harvnb|Chaput|2003|pp=[https://books.google.com/books?id=9qA_-Rkkq2AC&pg=PA182 182–183]}}</ref>}}

Various philosophical problems are associated with the ontological status of [[Virtual artifact|virtual objects]], such as a magic sword found inside a video game world. One perspective holds that such objects are illusory or unreal because they lack existence in the physical world outside the simulation. Another view maintains that they are real as digital objects with genuine existence and causal powers, residing within and being constituted by computational processes.<ref>{{multiref | {{harvnb|Chalmers|2022|loc=§ 6. What Is Reality?, §  11. Are Virtual Reality Devices Illusion Machines?}} | {{harvnb|Fernandes|2023|loc=§ Introduction}} }}</ref>

=== Worldviews and theories of everything ===
A [[worldview]] is a comprehensive framework for understanding reality and humanity's place within it. It comprises beliefs, ideas, and attitudes that form a background against which people interpret experiences, make decisions, and navigate life. Accordingly, worldviews address not only theoretical matters but also practical and evaluative outlooks about what matters and how one should act. Different worldviews offer distinct answers to existential questions about [[Meaning of life|meaning]], [[morality]], and the nature of reality, such as the contrast between [[religious]] and [[Secularity|secular]] worldviews.<ref>{{multiref | {{harvnb|Bunge|2010|pp=1–6}} | {{harvnb|McIvor|2008}} | {{harvnb|Wheeler|2020|loc=§ 1. Introduction to Worldviews}} }}</ref>

A theory of everything is a comprehensive explanatory scheme that integrates all knowledge into a consistent theoretical framework. Such theories aim at a unified explanation rather than a collection of isolated facts, for example, by identifying a limited number of basic constituents, categories, or principles as an explanatory basis of all phenomena. [[Theory of everything (philosophy)|Philosophical theories of everything]] consider a wide range of phenomena from diverse domains, including the nature of [[matter]] and [[mind]], mathematical truths, [[free will]], [[moral obligations]], and [[values]]. A key idea underlying this approach is to study the unrestricted whole by overcoming the boundaries of the restricted domains of other fields of inquiry, such as physics and psychology.<ref>{{multiref | {{harvnb|Hunt|1992|pp=219–221}} | {{harvnb|Søvik|2022|pp=3–6, 26}} | {{harvnb|White|2014|pp=3–9}} }}</ref> In physics, the term ''[[theory of everything]]'' has a more specific meaning, denoting a framework that unifies [[quantum physics]] with the [[theory of relativity]]. The theory of relativity describes macroscopic reality and the nature of [[gravitation]], while quantum physics describes microscopic reality and all known [[fundamental interactions]] except gravitation. Unification is required for areas where both domains overlap, such as [[black holes]], for which strong gravitational fields influence quantum behavior.<ref>{{multiref | {{harvnb|Stern|2000|pp=[https://books.google.com/books?id=buzuYtjU5o0C&pg=PA174 174–176]}} | {{harvnb|Sanchez|1992|pp=359–360}} }}</ref>

== In various fields ==
The concept of reality is relevant to many fields. In [[philosophy]], [[metaphysics]] and [[ontology]] study its nature and fundamental structure. They examine what it means for something to be real, how [[Entity|entities]] are divided into different [[categories of being]], and which entities exist at the most fundamental level.<ref>{{multiref | {{harvnb|Rescher|2018|pp=[https://books.google.com/books?id=jVyAEQAAQBAJ&pg=PA1 1–2]}} | {{harvnb|Lowe|2005a|p=671}} | {{harvnb|Koons|Pickavance|2017|pp=1–2}} }}</ref>

[[File:Referential theory of meaning.svg|thumb|alt=Diagram of the term "apple" and an arrow pointing to an apple|The [[philosophy of language]] examines how linguistic entities, such as the term ''apple'', can establish contact with reality by successfully referring to things in the world.<ref>{{harvnb|Robertson|2013|pp=[https://books.google.com/books?id=czr880lvAPIC&pg=PA189 189–190]}}</ref>]]

[[Epistemology]], another philosophical subdiscipline, explores how people can know reality. It investigates what [[knowledge]] is, how it originates, and what can or cannot be known.<ref>{{multiref | {{harvnb|Steup|Neta|2024|loc=Lead section, § 2. What is Knowledge?, § 6. The Limits of Cognitive Success}} | {{harvnb|Crumley II|2009|pp=16–17}} }}</ref> [[Phenomenology (philosophy)|Phenomenology]] analyzes the subjective structure of [[consciousness]]. It focuses on how individuals experience reality and how conscious states are [[Intentionality|intentional]] or directed towards entities other than themselves.<ref>{{multiref | {{harvnb|Schmitt|2006|loc=Lead section, § Intentionality}} | {{harvnb|Smith|2018|loc=Lead section}} }}</ref> The problem of [[reference]] is a similar topic in [[philosophy of mind]] and [[philosophy of language]]. It concerns the question of how mental and linguistic entities, such as [[thoughts]] and [[words]], can establish contact with reality by successfully referring to things in the world.<ref>{{multiref | {{harvnb|Blackburn|2005|pp=312}} | {{harvnb|Kim|2011|pp=23–26}} | {{harvnb|Robertson|2013|pp=[https://books.google.com/books?id=czr880lvAPIC&pg=PA189 189–190]}} }}</ref> Various other subfields of philosophy examine specific domains of reality. For example, [[value theory]] is concerned with the reality of [[values]],<ref>{{harvnb|Hirose|Olson|2015|pp=[https://books.google.com/books?id=uvzVBgAAQBAJ&pg=PA1 1–4]}}</ref> and the [[philosophy of mathematics]] explores in what sense [[mathematical objects]], like [[number]]s and [[Set (mathematics)|sets]], form part of reality.<ref>{{harvnb|Irvine|2009|p=[https://books.google.com/books?id=mbn35b2ghgkC&pg=PR9 ix–xi]}}</ref>

In the [[sciences]], [[physics]] studies the physical world and encompasses a broad range of phenomena. At the [[subatomic]] scale, [[particle physics]] focuses on [[elementary particles]] and their interactions. At the astronomical scale, [[cosmology]] analyzes the origin, structure, and development of the [[universe]] as a whole.<ref>{{multiref | {{harvnb|Perkowitz|2019|loc=§ Physics Subdivided}} | {{harvnb|Iliopoulos|Tomaras|2021|pp=[https://books.google.com/books?id=y2dHEAAAQBAJ&pg=PA1 1–2]}} }}</ref>

[[Psychology]] examines how individuals perceive, interpret, and respond to reality, including how mental processes construct models of reality and how [[illusions]] and [[Cognitive bias|biases]] distort understanding.<ref>{{multiref | {{harvnb|Bernstein|Nash|2006|pp=86, 117–120}} | {{harvnb|Gross|2020|pp=74, 242, 332–333}} }}</ref> It overlaps with the [[cognitive sciences]], which investigate how cognitive processes transform [[information]] about the world, and with [[neuroscience]], which studies the brain activities underlying such processes.<ref>{{harvnb|Friedenberg|Silverman|Spivey|2022|pp=2–3, 17–18}}</ref> In [[psychoanalytic theory]], the [[reality principle]] is a proposed mechanism that counteracts the [[Pleasure principle (psychology)|pleasure principle]], delaying immediate gratification when it collides with the demands of external reality.<ref>{{harvnb|Roussillon|2005}}</ref> [[Reality testing]] is another suggested psychological function in which individuals distinguish intrapsychic from external events to assess how their experience aligns with reality.<ref>{{harvnb|American Psychological Association|2018}}</ref>

[[Computer scientists]] discuss how systems of [[knowledge representation]] can organize information about reality and make it accessible to computational processes.<ref>{{multiref | {{harvnb|Sonneveld|Loening|1993|pp=[https://books.google.com/books?id=BbBBAAAAQBAJ&pg=PA188 188–189]}} | {{harvnb|Shapiro|2006|p=1}} }}</ref> Such data may be used in [[Computer simulation]]s to model real-world phenomena and predict outcomes. The [[simulation hypothesis]] is the view that the whole world and everything within it is a simulated reality, including humans. A related idea holds that information is the fundamental substance of reality.<ref>{{multiref | {{harvnb|Chalmers|2022|loc=§ 2. What Is the Simulation Hypothesis?}} | {{harvnb|Dodig-Crnkovic|2007|pp=[https://books.google.com/books?id=fTdhDQAAQBAJ&pg=PA263 263–267]}} }}</ref>

[[Anthropology]] examines diverse ways of life, including the question of how distinct [[cultures]] interpret reality. One strand of the field analyzes culture-specific worldviews and compares them across [[societies]].<ref>{{multiref | {{harvnb|Mendelson|2008|loc=Lead section}} | {{harvnb|Sheikh|2022|loc=§ Introductin, § From the Margins to the Center of Conflict Thinking}} }}</ref> [[Religion]] and [[theology]] are interested in the nature and existence of [[God]] or the divine. Some doctrines hold that God constitutes the most fundamental level of reality as the divine origin of all creation.<ref>{{harvnb|Meister|2014|pp=[https://link.springer.com/chapter/10.1057/9781137314758_3 19–20]}}</ref>

[[History]] studies historical reality primarily associated with the [[Human history|human past]]. Various [[historiographical]] debates address the question of whether a truly [[Objectivity (science)|objective]] account of the past is possible.<ref>{{multiref | {{harvnb|Collingwood|1993|p=[https://books.google.com/books?id=pTucAQAAQBAJ&pg=PA9 9]}} | {{harvnb|Kragh|1987|p=[https://books.google.com/books?id=OX7d7u_2rF4C&pg=PA41 41]}} | {{harvnb|Stanford|1998|pp=[https://books.google.com/books?id=PijhEAAAQBAJ&pg=PA50 50–53]}} }}</ref> In [[art history]], various [[Art style|styles]] address the problem of reality, including [[Realism (arts)|realism]], which seeks accurate representation of its subject matter, and [[surrealism]], which employs unexpected symbolism and irrational connections to reveal deeper layers associated with the [[unconscious mind]] and dreams.<ref>{{multiref | {{harvnb|Frazier|2000|pp=561, 658–659}} | {{harvnb|Sułkowski|Dacko-Pikiewicz|Szczepańska-Woszczyna|2025|loc=§ 9.5 Surrealist Marketing}} }}</ref>

== History ==
Various theories of the nature of reality originated in [[Ancient history|antiquity]]. Beginning in the first millennium BCE in [[Indian philosophy]], the [[Upanishads]] conceived [[Brahman]] as the supreme being and the source of all existence.<ref>{{multiref | {{harvnb|Perrett|2016|pp=[https://books.google.com/books?id=q7wwCwAAQBAJ&pg=PA7 7–10]}} | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} | {{harvnb|Andrea|Overfield|2015|pp=[https://books.google.com/books?id=x5-aBAAAQBAJ&pg=PA70 70–71]}} | {{harvnb|Naschak|2023|pp=[https://books.google.com/books?id=ZCOjEAAAQBAJ&pg=PA43 43–44]}}}}</ref> The school of [[Vaisheshika]] arose roughly in the 2nd century BCE and developed a system of six fundamental categories of being.<ref>{{multiref | {{harvnb|Kumar|2019|pp=[https://books.google.com/books?id=Jr2YDwAAQBAJ&pg=PA34 34–36]}} | {{harvnb|Leaman|2002|p=269}} | {{harvnb|Westerhoff|2019|loc=§ Three important systems of categories: Vaiśeṣika}} }}</ref> [[Samkhya]], another school of [[Hindu philosophy]] systematically formulated around 350 CE, proposed a [[dualistic]] framework, describing reality as the interplay of two principles: [[Purusha|pure consciousness]] and [[Prakriti|matter]].<ref>{{multiref | {{harvnb|Ruzsa|loc=Lead Section}} | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} }}</ref> In the [[Chinese philosophy|Chinese tradition]], [[Taoist]] thought emerged roughly in the 6th century BCE and understood the [[Tao]] as the all-pervasive, ineffable source of all reality.<ref>{{multiref | {{harvnb|Littlejohn|loc=§ 5. Fundamental Concepts in the Daodejing}} | {{harvnb|Dynes|2016|pp=[https://books.google.com/books?id=pxjOEAAAQBAJ&pg=PA60 60–61]}} | {{harvnb|Wang|Bao|Guan|2020|p=[https://books.google.com/books?id=gSfXDwAAQBAJ&pg=PA3 3]}} }}</ref>

[[File:Alpharabius in Liber Chronicarum 1493 AD.png|thumb|upright=0.8|alt=Black-and-white image of an elderly man with a long beard wearing a robe|Various medieval thinkers, such as [[Al-Farabi]], held that God is the ground of all existence.<ref>{{multiref | {{harvnb|Morley|loc=§ 1.b. Early Christian Thought, § 1.c. Medieval Thought}} | {{harvnb|Carroll|2007|pp=678–686}} }}</ref>]]

In [[ancient Greek philosophy]] starting in the 6th century BCE, the [[pre-Socratics]] discussed the [[Arche|first principles]] from which all things arise.<ref>{{multiref | {{harvnb|Hancock|2006|p=183}} | {{harvnb|Hamlyn|2005|p=590}} | {{harvnb|Kirk|2004|pp=[https://books.google.com/books?id=uewoLyIw_DQC&pg=PA308 308–310]}} }}</ref> [[Leucippus]] ({{floruit|5th century BCE}}) and his student [[Democritus]] ({{circa|460|370 BCE}}) held that reality is fundamentally [[Atomism|composed of indivisible units]], which they termed ''atoms''.<ref>{{harvnb|Webel|2021|pp=34–35}}</ref> [[Plato]] ({{circa|427|347 BCE}}) argued for the existence of a [[Theory of Forms|realm of eternal forms or ideas]] in addition to the material world of mutable entities.<ref>{{multiref | {{harvnb|Hancock|2006|pp=184–185}} | {{harvnb|Hamlyn|2005|p=590}} | {{harvnb|Graham|loc=§ 3b. Metaphysics}} }}</ref> His student [[Aristotle]] (384–322 BCE) proposed a [[Categories (Aristotle)|system of ten categories]] describing the fundamental constituents of reality.<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.1 Aristotelian Realism}} | {{harvnb|Studtmann|2024|loc=§ 2. The Ten-Fold Division}} | {{harvnb|Wardy|1998|loc=§ 1. Categories in Aristotle}} }}</ref> Inspired by Plato's realm of forms, [[Plotinus]] ({{circa|204|270 CE}}) identified [[Neoplatonism#The One|the One]] as the supreme principle underlying all of reality.<ref>{{multiref | {{harvnb|Hancock|2006|pp=187–188}} | {{harvnb|Hamlyn|2005|pp=590–591}} | {{harvnb|Graham|loc=§ 5. Post-Hellenistic Thought}} }}</ref>

[[File:Raja Ravi Varma - Sankaracharya - cropped.png|thumb|upright=.8|alt=Painting of a man sitting cross-legged wearing a red robe|The school of [[Advaita Vedanta]], as developed by [[Adi Shankara]], holds that the world of everyday appearances is an illusion and that only the underlying Brahman has absolute reality.<ref>{{multiref | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} | {{harvnb|Perrett|2016|loc=§ The Medieval Period of Indian Philosophy}} | {{harvnb|Dalal|2021|loc=Lead Section, § 2.3 Two-Tiered Reality}} | {{harvnb|Rangaswami|2012|p=[https://books.google.com/books?id=2snhxaaWDAYC&pg=PA114 114]}} }}</ref>]]

During the [[medieval period]], many thinkers understood God as the most fundamental reality and the source of all [[Creationism|creation]]. Variations of this idea are found in the [[Christianity|Christian tradition]], proposed by philosophers such as [[Augustine of Hippo]] (354–430) and [[Thomas Aquinas]] (1225–1274), and in the [[Islam|Islamic tradition]], explored by thinkers such as [[Al-Farabi]] ({{circa|870|950}}) and [[Avicenna]] (980–1037).<ref>{{multiref | {{harvnb|Morley|loc=§ 1.b. Early Christian Thought, § 1.c. Medieval Thought}} | {{harvnb|Carroll|2007|pp=678–686}} }}</ref> Another central topic in this period was the [[problem of universals]], with realists, conceptualists, and nominalists discussing whether universals exist as mind-independent entities, as mental entities, or not at all.<ref>{{multiref | {{harvnb|Inwagen|2023}} | {{harvnb|MacLeod|Rubenstein|loc=Lead Section, § 3. Versions of Anti-Realism}} | {{harvnb|Bigelow|1998a|loc=§ 4. Nominalism and Realism}} }}</ref> In Hindu philosophy, the school of [[Advaita Vedanta]] emerged in the 8th century and held that the [[Maya (religion)|world of everyday appearances is an illusion]], contrasting it with the ultimate reality of Brahman.<ref>{{multiref | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} | {{harvnb|Perrett|2016|loc=§ The Medieval Period of Indian Philosophy}} | {{harvnb|Dalal|2021|loc=Lead Section, § 2.3 Two-Tiered Reality}} | {{harvnb|Rangaswami|2012|p=[https://books.google.com/books?id=2snhxaaWDAYC&pg=PA114 114]}} }}</ref> In China, beginning roughly in the 9th century, [[Neo-Confucianism]] maintained that reality has a rational order expressed in the principle ''[[Li (neo-Confucianism)|Li]]'', which acts as a ground of being.<ref>{{multiref | {{harvnb|Berthrong|loc=Lead Section, § 4. Traits, Themes and Motifs}} | {{harvnb|Wu|2022|p=[https://books.google.com/books?id=zRVmEAAAQBAJ&pg=PA56 56]}} | {{harvnb|Smart|2008|p=99}}}}</ref>

In [[early modern philosophy]], [[René Descartes]] (1596–1650) proposed [[substance dualism]], arguing that reality is made up of two kinds of entities: [[matter]] and [[mind]].<ref>{{multiref | {{harvnb|Hamlyn|2005|p=591}} | {{harvnb|Dehsen|2013|p=[https://books.google.com/books?id=cU7cAAAAQBAJ&pg=PA51 51]}} }}</ref> [[Baruch Spinoza]] (1632–1677) rejected Descartes's dualism, holding instead that the world consists of a single entity, which he called "God or nature".<ref>{{multiref | {{harvnb|Hancock|2006|p=190}} | {{harvnb|Hamlyn|2005|p=591}} }}</ref> [[Gottfried Wilhelm Leibniz]] (1646–1716) examined the relation between reality and possibility, suggesting that [[possible worlds]] are ideas in God's mind, while only the actual world is realized, chosen by God as the best possible world.<ref>{{harvnb|Brown|Chiek|2016|pp=[https://books.google.com/books?id=i9zMDQAAQBAJ&pg=PA2 2–3]}}</ref> Analyzing human experience, [[John Locke]] (1632–1704) distinguished [[Primary–secondary quality distinction|primary from secondary qualities]] and argued that only primary qualities correspond to objective features of reality.<ref>{{multiref | {{harvnb|Mulder|loc=Lead section, § 2.a. Can We Know Objective Reality?}} | {{harvnb|Bunge|2006|p=42}} }}</ref> In his [[classical mechanics]], [[Isaac Newton]] (1643–1727) conceived the universe as a [[Causal determinism|deterministic]] system governed by universal [[laws of motion]].<ref>{{multiref | {{harvnb|McCauley|1997|p=[https://books.google.com/books?id=PxytO6eByI8C&pg=PA21 21]}} | {{harvnb|Mossman|2014|p=[https://books.google.com/books?id=ecxLBAAAQBAJ&pg=PA19 19]}} }}</ref> [[George Berkeley]] (1685–1753) developed a comprehensive form of [[subjective idealism]], asserting that objects exist only as ideas in minds, expressed in his slogan "to be is to be perceived".<ref>{{harvnb|Cowan|Spiegel|2016|pp=[https://books.google.com/books?id=Ixk2CwAAQBAJ&pg=PA1 1–3]}}</ref>

[[File:Russell1907-2.jpg|thumb|alt=Black-and-white photo of a man with a mustache wearing a suit|upright=.8|In his logical atomism, [[Bertrand Russell]] conceived reality as a multitude of basic facts.<ref>{{harvnb|Livingston|2001|pp=30–36}}</ref>]]

[[Immanuel Kant]] (1724–1804) rejected the possibility of objective knowledge of the things in themselves, arguing instead that [[Transcendental idealism|all experience is shaped by the innate structures]] of human [[cognition]].<ref>{{multiref | {{harvnb|Mulder|loc=§ 2.d. Skepticism Regarding Knowledge of Objective Reality}} | {{harvnb|Bunge|2006|pp=31, 42}} | {{harvnb|Brinkmann|2010|pp=[https://books.google.com/books?id=vuT31alSlQwC&pg=PA41 41–45]}} }}</ref> Responding to Kant's philosophy, the [[German idealists]] sought a unifying principle as the foundation of all reality.<ref>{{multiref | {{harvnb|Hancock|2006|p=193}} | {{harvnb|Hamlyn|2005|p=592}} | {{harvnb|Critchley|2001|p=[https://books.google.com/books?id=syhsLJ1eMOEC&pg=PA31 31]}} }}</ref> A similar outlook was adopted by [[Francis Herbert Bradley]] (1846–1924), who conceived [[Absolute (philosophy)|the absolute]] as the all-inclusive totality of being.<ref>{{multiref | {{harvnb|Hancock|2006|p=193}} | {{harvnb|Hamlyn|2005|p=592}} | {{harvnb|Grayling|2019|loc=§ Idealism}} }}</ref> By contrast, [[Arthur Schopenhauer]] (1788–1860) criticized German idealism and held that [[Voluntarism (philosophy)|a blind, irrational will is the underlying principle of reality]].<ref>{{multiref | {{harvnb|Grayling|2019|loc=§ Schopenhauer}} | {{harvnb|Janaway|1999|pp=[https://academic.oup.com/book/2954/chapter-abstract/143638920?redirectedFrom=fulltext 248–249]}} | {{harvnb|Barua|2018|pp=[https://books.google.com/books?id=mqVFDwAAQBAJ&pg=PA2 2–3]}} }}</ref>

At the beginning of the 20th century, [[Bertrand Russell]] (1872–1970) and [[G. E. Moore]] (1873–1958) drew on [[common sense]] and empirical science to oppose [[idealism]], emphasizing that the world exists independently of the mind.<ref>{{multiref | {{harvnb|Griffin|2013|pp=383, 396, 399–402}} | {{harvnb|Peters|2021|pp=[https://books.google.com/books?id=UakWEAAAQBAJ&pg=PA31 31–32]}} }}</ref> Alongside his student [[Ludwig Wittgenstein]] (1889–1951), Russell developed [[logical atomism]], which characterizes reality as a multitude of basic facts.<ref>{{harvnb|Livingston|2001|pp=30–36}}</ref> [[Alfred North Whitehead]] (1861–1947) advanced a different outlook that frames reality as an organic whole [[Process philosophy|made up of processes]].<ref>{{multiref| {{harvnb|MacLean|2012|p=[https://books.google.com/books?id=6n-hQpt6r3sC&pg=PA51 51]}} | {{harvnb|Palmer|1998|p=[https://books.google.com/books?id=ZT2pI9IMiYUC&pg=PA175 175]}}}}</ref> 

[[Alexius Meinong]] (1853–1920) maintained that the concept of being is broader than the concept of reality since it includes [[Nonexistent objects|non-existent entities]], such as merely possible and incomplete objects.<ref>{{harvnb|Marek|2024|loc=Lead section, § 2. Meinong on Philosophy, § 5. Object Theory — Ontology beyond Being and Non-Being}}</ref> Influenced by Kant, [[Edmund Husserl]] (1859–1938) argued that reality is tied to consciousness as an [[intersubjective]] correlate of experience that cannot be reduced to a wholly mind-independent substrate.<ref>{{harvnb|Zahavi|2025|loc=§ 3. The Transcendental Turn: Epoché, Phenomenological Reduction, and Transcendental Idealism}}</ref> [[Nicolai Hartmann]] (1882–1950) proposed a hierarchical model of reality, dividing the world into four levels: the inanimate, the biological, the psychological, and the spiritual.<ref>{{harvnb|Poli|2011|pp=[https://books.google.com/books?id=1Qya55bssVQC&pg=PA1 1, 11, 21–22]}}</ref> Inspired by Leibniz, [[David Lewis (philosopher)|David Lewis]] (1941–2001) developed [[modal realism]], maintaining that possible worlds are as real as the actual world.<ref>{{multiref | {{harvnb|Menzel|2025|loc=§ 2. Three Philosophical Conceptions of Possible Worlds}} | {{harvnb|Parent|loc=Lead section, § 2. Lewis' Realism}} }}</ref>

In physics, [[Albert Einstein]] (1879–1955) developed the [[theory of relativity]], which treats [[spacetime|space and time]] as interwoven dimensions whose [[geometry]] is [[Curved spacetime|curved by matter and energy]].<ref>{{multiref | {{harvnb|Weinert|2004|pp=[https://books.google.com/books?id=-R4ANHu-csMC&pg=PA130 130–131]}} | {{harvnb|Petkov|2014|pp=[https://books.google.com/books?id=Gi9nBAAAQBAJ&pg=PA153 153]}} }}</ref> [[Quantum mechanics]] originated in the works of [[Niels Bohr]] (1885–1962), [[Werner Heisenberg]] (1901–1976), and [[Erwin Schrödinger]] (1887–1961). It revolutionized the scientific understanding of microscopic reality, revealing that particles can exhibit [[Wave–particle duality|wave-like behavior]], that certain physical quantities, like energy, take only [[Quantum|discrete values]] rather than a continuous range, and that measurement outcomes are inherently [[Probability|probabilistic]].<ref>{{harvnb|Polkinghorne|2002|pp=[https://books.google.com/books?id=Zp7P8LayJJgC&pg=PR11 xi–xii, 11–12, 17–18, 25–26]}}</ref> In the course of 20th-century [[philosophy of science]], [[scientific realism]] gained prominence, arguing that the best scientific theories provide an accurate description of a mind-independent world.<ref>{{multiref | {{harvnb|Liston|loc=Lead section, § 5. Scientific Realism}} | {{harvnb|Saatsi|2017|pp=[https://books.google.com/books?id=SFEPEAAAQBAJ&pg=PA2 2]}} }}</ref>

== References ==
=== Notes ===
{{notelist|30em}}

=== Citations ===
{{reflist|30em}}

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{{refend}}

== External links ==
{{Sister project links|Reality}}

{{Philosophy topics}}
{{metaphysics}}
{{Authority control}}

[[Category:Reality| ]]
[[Category:Concepts in metaphysics]]
[[Category:Concepts in epistemology]]
[[Category:Concepts in logic]]
[[Category:Concepts in the philosophy of language]]
[[Category:Concepts in the philosophy of mind]]
[[Category:Concepts in the philosophy of science]]