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{{Short description|Metaphysics concept covering the divide between two types of entities}}
{{Redirect|Abstract entity|conceptual abstraction|Abstraction|the album by Kiana|Kiana (band)#Discography{{!}}Abstract Entity}}

In [[philosophy]] and [[the arts]], a fundamental distinction exists between '''abstract''' and '''concrete''' entities. While there is no [[Consensus decision-making|universally accepted]] definition, common examples illustrate the difference: [[number]]s, [[set (mathematics)|sets]], and [[idea]]s are typically classified as abstract objects, whereas [[plant]]s, [[dogs]], and [[planet]]s are considered concrete objects.<ref name="Rosen">{{cite web |last1=Rosen |first1=Gideon |title=Abstract Objects |url=https://plato.stanford.edu/entries/abstract-objects/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=4 January 2021 |date=2020}}</ref>

Philosophers have proposed several criteria to define this distinction:

# ''Spatiotemporal existence'' – Abstract objects exist outside [[space-time]], while concrete objects exist within space-time.
# ''Causal influence'' – Concrete objects can cause and be affected by other entities (e.g., a rock breaking a window), whereas abstract objects (e.g., the number 2) lack causal powers and do not cause anything to happen in the physical world.
# ''Metaphysical relation'' – In [[metaphysics]], concrete objects are specific, individual things ([[Particular|particulars]]), while abstract objects represent general concepts or categories ([[Universal (metaphysics)|universals]]).
# ''Ontological domain'' – Concrete objects belong to the physical realm (or both the physical and mental realms), whereas abstract objects belong to neither.<ref>{{cite book |last1=Honderich |first1=Ted |title=The Oxford Companion to Philosophy |date=2005 |publisher=Oxford University Press |url=https://philpapers.org/rec/HONTOC-2 |chapter=abstract entities}}</ref><ref>{{cite book |last1=Craig |first1=Edward |title=Routledge Encyclopedia of Philosophy |date=1996 |publisher=Routledge |url=https://philpapers.org/rec/BEAREO |chapter=Abstract objects}}</ref><ref name="A Glossary of Literary Terms">{{cite book|title=A Glossary of Literary Terms|url=https://books.google.com/books?id=SUEtEa9nUWQC&pg=PA60|access-date=18 September 2012|isbn=978-0495898023|last1=Abrams|first1=Meyer Howard|last2=Harpham|first2=Geoffrey Galt|year=2011| publisher=Cengage Learning }}</ref> 

Another view is that it is the distinction between contingent existence versus necessary existence; however, philosophers differ on which type of existence here defines abstractness, as opposed to concreteness. Despite this diversity of views, there is broad agreement concerning most objects as to whether they are abstract or concrete,<ref name="Rosen"/> such that most interpretations agree, for example, that rocks are concrete objects while numbers are abstract objects.

Abstract objects are most commonly used in [[philosophy]], particularly metaphysics, and [[semantics]]. They are sometimes called '''''abstracta''''' in contrast to '''''concreta'''''. The term ''abstract object'' is said to have been coined by [[Willard Van Orman Quine]].<ref>{{cite book|last=Armstrong|first=D. M.|title=Sketch for a systematic metaphysics|year=2010|publisher=Oxford University Press|location=Oxford|isbn=9780199655915|page=2}}</ref> [[Abstract object theory]] is a discipline that studies the nature and role of abstract objects. It holds that properties can be related to objects in two ways: through exemplification and through encoding. Concrete objects exemplify their properties while abstract objects merely encode them. This approach is also known as the [[dual copula strategy]].{{sfn|Zalta|1983|p=33}}

==In philosophy<!--'Third Realm (Frege)' redirects here-->==
The [[type–token distinction]] identifies physical objects that are tokens of a particular type of thing.<ref>Carr, Philip (2012) "The Philosophy of Phonology" in ''Philosophy of Linguistics'' (ed. Kemp, Fernando, Asher), Elsevier, p. 404</ref>  The "type" of which it is a part is in itself an abstract object. The abstract–concrete distinction is often introduced and initially understood in terms of [[paradigm|paradigmatic]] examples of objects of each kind:

{| class="wikitable"
|-
|+ Examples of abstract and concrete objects
|-
!'''Abstract'''
!'''Concrete'''
|-
| Tennis
| A tennis match
|-
| Redness
| Red light reflected off of an apple and hitting one's eyes
|-
| Five
| Five cars
|-
| Justice
| A just action
|-
| Humanity (the property of being human)
| Human population (the set of all humans)
|-
|}

Abstract objects have often garnered the interest of philosophers because they raise problems for popular theories. In [[ontology]], abstract objects are considered problematic for [[physicalism]] and some forms of [[Metaphysical naturalism|naturalism]]. Historically, the most important ontological dispute about abstract objects has been the [[problem of universals]]. In [[epistemology]], abstract objects are considered problematic for [[empiricism]]. If abstracta lack causal powers and spatial location, how do we know about them? It is hard to say how they can affect our sensory experiences, and yet we seem to agree on a wide range of claims about them.

Some, such as [[Ernst Mally]],<ref>[https://mally.stanford.edu/mally.html Ernst Mally – The Metaphysics Research Lab]</ref> [[Edward Zalta]]<ref name=SEP/> and arguably, [[Plato]] in his [[Theory of Forms]],<ref name=SEP/> have held that abstract objects constitute the defining subject matter of [[metaphysics]] or philosophical inquiry more broadly. To the extent that philosophy is independent of empirical research, and to the extent that empirical questions do not inform questions about abstracta, philosophy would seem especially suited to answering these latter questions.

In [[modern philosophy]], the distinction between abstract and concrete was explored by [[Immanuel Kant]]<ref>''[[Critique of Pure Reason|KrV]]'' A51/B75–6. See also: Edward Willatt, ''Kant, Deleuze and Architectonics'', Continuum, 2010 p. 17: "Kant argues that cognition can only come about as a result of the union of the abstract work of the understanding and the concrete input of sensation."</ref> and [[G. W. F. Hegel]].<ref>Georg Wilhelm Friedrich Hegel: ''[[The Science of Logic]]'', Cambridge University Press, 2010, p. 609. See also: Richard Dien Winfield, ''Hegel's Science of Logic: A Critical Rethinking in Thirty Lectures'', Rowman & Littlefield Publishers, 2012, p. 265.</ref>

[[Gottlob Frege]] said that abstract objects, such as propositions, were members of a third realm,<ref>[[Gottlob Frege]], "Der Gedanke. Eine logische Untersuchung", in: ''Beiträge zur Philosophie des deutschen Idealismus'' 1 (1918/19), pp. 58–77; esp. p. 69.</ref> different from the external world or from internal [[consciousness]].<ref name="Rosen" /> (See [[Popper's three worlds]].)

===Abstract objects and causality===
Another popular proposal for drawing the abstract–concrete distinction contends that an object is abstract if it lacks [[causality|causal]] power. A causal power has the ability to affect something causally. Thus, the empty set is abstract because it cannot act on other objects. One problem with this view is that it is not clear exactly what it is to have causal power. For a more detailed exploration of the abstract–concrete distinction, see the relevant ''[[Stanford Encyclopedia of Philosophy]]'' article.<ref name=SEP>{{cite SEP |url-id=abstract-objects |title=Abstract Objects |last=Rosen |first=Gideon}}</ref>

===Quasi-abstract entities<!--'Quasi-abstract' redirects here-->===
In the 2010s, there was some philosophical interest in the development of a third category of objects known as the '''quasi-abstract'''<!--boldface per WP:R#PLA-->. Quasi-abstract objects have drawn particular attention in the area of [[social ontology]] and [[documentality]]. Some argue that the over-adherence to the [[Platonism|platonist]] duality of the concrete and the abstract has led to a large category of social objects having been overlooked or rejected as [[Nonexistent object|nonexistent]] because they exhibit characteristics that the traditional duality between concrete and abstract regards as incompatible.<ref>B. Smith (2008), "Searle and De Soto: The New Ontology of the Social World". In ''The Mystery of Capital and the Construction of Social Reality''. Open Court.</ref> Specifically, the ability to have temporal location, but not spatial location, and have causal agency (if only by acting through representatives).<ref>{{cite journal |first1=E. H. |last1=Robinson |url=http://www.edwardheath.net/wp-content/uploads/2013/01/Social_Agentivity.pdf |title=A Theory of Social Agentivity and Its Integration into the Descriptive Ontology for Linguistic and Cognitive Engineering |journal=[[International Journal on Semantic Web and Information Systems]] |volume=7 |issue=4 |date=2011 |pages=62–86 |doi=10.4018/ijswis.2011100103 |url-status=dead |archive-url=https://web.archive.org/web/20170810075924/http://www.edwardheath.net/wp-content/uploads/2013/01/Social_Agentivity.pdf |archive-date= Aug 10, 2017 }}</ref> These characteristics are exhibited by a number of social objects, including states of the international legal system.<ref>E. H. Robinson (2014), "A Documentary Theory of States and Their Existence as Quasi-Abstract Entities", ''Geopolitics'' '''19''' (3), pp. 1–29.</ref>

==Concrete and abstract thought in psychology==
{{unreferenced section|date=January 2021}}
[[Jean Piaget]] uses the terms "concrete" and "formal" to describe two different types of learning. Concrete thinking involves facts and descriptions about everyday, tangible objects, while abstract ([[Formal Operational#Formal operational stage|formal operational]]) thinking involves a mental process.
{| class="wikitable"
|-
! Abstract idea
! Concrete idea

|-
| Dense things sink.
| It will sink if its density is greater than the density of the fluid.
|-
| You breathe in oxygen and breathe out carbon dioxide.
| Gas exchange takes place between the air in the alveoli and the blood.

|-
| Plants get water through their roots.
| Water diffuses through the cell membrane of the root hair cells.

|}

==See also==
{{Columns-list|colwidth=22em|
* [[Abstract structure]]
* [[Conceptual framework]]
* [[Emic and etic]]
* [[Incorporeality]]
* [[Nominalism]]
* [[Non-physical entity]]
* [[Observation]]
* [[Philosophy of mathematics]]
* [[Platonic realm]]
* [[Platonism]]
* [[Present]]
* [[Problem of universals]]
}}

==References==
{{Reflist}}

==Sources==
* {{cite book
|last=Zalta
|first=Edward N.
|author-link=Edward N. Zalta
|year=1983
|title=Abstract Objects: An Introduction to Axiomatic Metaphysics
|series=Synthese Library
|volume=160
|location=Dordrecht, Netherlands
|publisher=D. Reidel Publishing Company
|isbn=978-90-277-1474-9
}}

==External links==
* {{PhilPapers|category|abstract-objects}}
* [http://www.newadvent.org/cathen/11090c.htm Nominalism, Realism, Conceptualism], from ''[[The Catholic Encyclopedia]]''
* [http://www.writingforresults.net/Acro_3/2_cntnt/2_abstct.pdf  Abstract vs. Concrete in Writing], from Writing for Results

{{Metaphysics}}
{{Philosophy of mind}}
{{Authority control}}

[[Category:Abstract object theory]]
[[Category:Abstraction]]
[[Category:Cognition]]
[[Category:Metaphysical properties]]
[[Category:Consciousness]]
[[Category:Metaphysical theories]]
[[Category:Metaphysics of mind]]
[[Category:Theory of mind]]
[[Category:Syntax–semantics interface]]