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{{Short description|Class of key on a computer keyboard}}
{{Refimprove|date=July 2008}}
In [[computing]], a '''modifier key''' is a special key (or combination) on a [[computer keyboard]] that temporarily modifies the normal action of another key when pressed together. By themselves, modifier keys usually do nothing; that is, pressing any of the {{keypress|[[Shift key|Shift]]}}, {{keypress|[[Alt key|Alt]]}}, or {{Key press|[[Control key|Ctrl]]}} keys alone does not (generally)<!-- Alt redirects the "attention" from the current area (as it's for me), Ctrl can be set to highlight the cursor's position. --> trigger any action from the computer. They are commonly used in defined sequences of keys with another keys to trigger a specific action. These sequences are called [[Keyboard shortcut|keyboard shortcuts]].

For example, in most [[keyboard layout]]s the Shift key combination {{keypress|Shift|A}} will produce a capital letter "A" instead of the default lower-case letter "a" (unless in [[Caps Lock]] or [[Shift lock]] mode). A combination of {{keypress|Alt|F4}} in [[Microsoft Windows]] will trigger the shortcut for closing the [[active window]]; in this instance, Alt is the modifier key. In contrast, pressing just {{keypress|Shift}} or {{keypress|Alt}} will probably do nothing unless assigned a specific function in a particular program (for example, activating input aids or the toolbar of the active window in Windows).

[[User interface]] expert [[Jef Raskin]] coined the term "[[Mode (user interface)|quasimode]]" to describe the state a computer enters into when a modifier key is pressed.

== History ==
{{Stub section|date=June 2024}}

==Modifier keys on personal computers==
The most common are:
* {{key top|Shift}}
* {{key top|Ctrl}} ('''C'''on'''tr'''o'''l''')
* {{key top|Alt}} ('''Alt'''ernate) – also labelled {{key top|Option}} on [[Apple keyboards]].
* {{key top|AltGr}} ('''Alt'''ernate '''Gr'''aphic)
* {{key top|Meta}} – Meta key, found on MIT, Symbolics, and Sun Microsystems keyboards.
* {{Key top|Hyper}} – Hyper key, found on the [[Space-cadet keyboard]]
* {{key top|Super}} – Super key, found on MIT, Symbolics, Linux, and BSD keyboards.
* {{key top|Win|3=true}} (Windows logo) – found on Windows keyboards.
* {{key top|Cmd}} – Command key, found on Apple keyboards. On older keyboards labelled {{key top|Apple}} (Apple logo).
* {{key top|Fn}} ('''F'''unctio'''n''') – often present on small-layout keyboards, or keyboard where the top row of function keys have multimedia functions like controlling volume attached.

The (Sun) Meta key, Windows key, (Apple) Cmd key, and the analogous "Amiga key" ({{keypress|{{math|'''''A'''''}}}}) on [[Amiga]] computers, are usually handled equivalently. Under the Linux operating system, the desktop environment [[KDE]] calls this key [[Meta key|Meta]], while [[GNOME]] calls this key, neutrally, [[Super key (keyboard button)|Super]]. This could be considered confusing, since the original [[space-cadet keyboard]] and the [[X Window System]] recognize a "{{keypress|Meta}}" modifier distinct from "{{keypress|Super}}".

The [[ZX Spectrum]] has a Symbol Shift key in addition to Caps Shift. This was used to access additional punctuation and keywords.

The [[MSX]] computer keyboard, besides Shift and Control, also included two special modifier keys, Code and Graph. In some models, as in the Brazilian [[Gradiente Expert]], the Code and Graph keys are labelled "{{keypress|L Gra}}" and "{{keypress|R Gra}}" (Left and Right Graphics). They are used to select special graphic symbols and extended characters.

Likewise, the [[Commodore 64]] and other Commodore computers had the Commodore key at the bottom left of the keyboard.

Compact keyboards, such as those used in [[laptop]]s, often have a [[Fn key]] to save space by combining two functions that are normally on separate keys.  On laptops, pressing {{keypress|Fn}} plus one of the function keys, e.g., F2, often control hardware functions. Keyboards that lack a dedicated numeric keypad may mimic its functionality by combining the Fn key with other keys.

The [[Massachusetts Institute of Technology|MIT]] [[space-cadet keyboard]] had additional Top and Front modifier keys. Combined with standard modifiers, it could enter as many as 8,000 different characters.

Specialist typesetting machines, and word processors such as the [[Redactron]], sometimes used multiple modifier keys to trigger mode changes e.g. for emboldened text or justification changes. This approach gradually became obsolete after software based on commodity hardware and operating systems adopted the [[WIMP (computing)|WIMP]] metaphor which provided drop-down menus etc.

===Accented characters===
Some non-English language keyboards have special keys to produce [[diacritic|accented]] modifications of the standard Latin-letter keys. In fact, the standard British [[keyboard layout]] includes an accent key on the top-left corner to produce àèìòù, although this is a two step procedure, with the user pressing the accent key, releasing, then pressing the letter key. These kinds of keys are called [[dead key]]s. The [[AltGr key|AltGr]] modifier produces the áéíóú sequence, or in conjunction with the Shift key, ÁÉÍÓÚ. Keyboards of some languages simply include the accented characters on their own keys. Some keyboards also have a [[Compose key]] for typing accented and other special characters.  By pressing {{keypress|Compose}}, and then two other keys, something similar to a combination of the glyphs of the two previous keys will appear on the screen.

== Modifier only ==
It is possible to use a modifier key as a normal key.

In 2005 macOS app [[Quicksilver (software)|Quicksilver]] introduced a feature called 'Modifier-only Activation'. If a modifier key (Command) was pressed for a short duration (under 300ms) then released with no other key being pressed, this was taken as a 'trigger'.

In 2012 this kind of use of a Modifier key appeared in Apple's 'Dictation preferences' under [[OS X Mountain Lion]], where Apple introduced options like 'Press Right Command Key twice' to launch dictation.

This functionality was further increased in macOS Sequoia (2024) with the addition of modifier only keys to be used alone to activate shortcuts such as 'Show Desktop, including Left Command, Left Option, Left Control, Left Shift, Right Command, Right Control, Right Option, Right Shift, fn. This effectively gives users 9 extra keys to activate shortcuts.

== Dual-role keys ==
It is also possible to use (with some utility software) one key both as a normal key and as a modifier.

For example, you can use the {{keypress|space bar}} both as a normal Space bar and as a Shift. Intuitively, it will act as a standard Space when you want a whitespace, and a Shift when you want it to act as a shift. I.e. when you simply press and release it, it is the usual space, but when you press other keys, say {{keypress|X}}, {{keypress|Y}} and {{keypress|Z}}, while holding down the {{keypress|space}}, then they will be treated as {{keypress|shift}} plus X, Y and Z. 

The above example is known as "SandS", standing for "Space and Shift" in Japan.<ref>{{Cite web
|url=http://hp.vector.co.jp/authors/VA002116/sands/
|title=SandS機能お試しアプレット
|author=K. Kimura
|language=ja
|date=2001-04-15
|archive-url=https://web.archive.org/web/20020215203809/http://hp.vector.co.jp/authors/VA002116/sands/
|archive-date=2002-02-15
|access-date=2011-11-30}}
</ref> But any number of any combinations are possible.<ref>{{Cite web
|url=https://gitlab.com/at-home-modifier/at-home-modifier-evdev/wikis/home
|title=At home modifier – Home
|access-date=2015-04-14}}</ref>

To press shift+space in the previous example, you need in addition to a space/shift dual role key, one of (a) another space/shift key, (b) a usual shift, or (c) a usual space key.

==See also==
* [[Bucky bit]]
* [[Control character]]
* [[Function key]]
* [[Keyboard layout]]
* [[Space-cadet keyboard]]
* [[Table of keyboard shortcuts]]
* [[Emacs pinky]] - [[repetitive strain injury]] developed by too much use of control key, notably for [[Emacs]] users.

== References ==
<references/>

==External links==
* [http://www.catb.org/jargon/html/B/bucky-bits.html Bucky bits in the Jargon file]

{{keyboard keys}}

{{DEFAULTSORT:Modifier Key}}
[[Category:Computer keys]]
[[Category:User interface techniques]]

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