Modifier key

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 ⇧ Shift, Alt, or Ctrl keys alone does not (generally) trigger any action from the computer.

For example, in most keyboard layouts the Shift key combination ⇧ 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 Alt+F4 in Microsoft Windows will close the active window; in this instance, Alt is the modifier key. In contrast, pressing just ⇧ Shift or 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 "quasimode" to describe the state a computer enters into when a modifier key is pressed.

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Dual-role keys

It is possible to use (with some utility software) one key both as a normal key and as a modifier.

For example, you can use the 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 X, Y and Z, while holding down the space, then they will be treated as ⇧ Shift plus X, Y and Z.

The above example is known as "SandS", standing for "Space and Shift" in Japan. But any number of any combinations are possible.

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.

External links

• Bucky bits in the Jargon file