From Wikipedia, the free encyclopedia

A dead key is a key on a typewriter or a computer keyboard that produces no output when it is pressed, but modifies the output of the next key pressed after it. For example, Option-` + e produces è on the Macintosh.

Dead keys are commonly used to generate letters with accents (diacritics), because that way one does not need one key for each possible combination of letter and accent, but only one key for each accent (the dead key) plus the usual letter keys.

For example, if a keyboard has a dead key "´", the French character e accent aigu (é) can be generated by pressing first "´", then "e". Usually pressing a dead key followed by space produces the character denoted by the dead key; e.g. "¨" + space results in "¨".

By construction, this has no restrictions on a typewriter, so you could accentuate an "f" for example. On the other hand, computers often do not work this way; "´" + "f" results in "´f".

In many text processing programs, dead keys are typed using the Ctrl key with the punctuation mark that looks most like the accent. In the X Window System, the AltGr key has this function.

With the advent of Unicode character encoding it is possible to combine any available diacritical mark with any other character. The "combining diacritical marks" can be found in Unicode space U+0300–U+036F. For example, you can combine "˜" (U+0303 Combining Tilde) with "p" so you get "p̃", whether this makes sense or not.

More exotically, you can combine " ̐" (U+0310 Combining Candrabindu) with "∞" so you get "∞̐".

Old computer systems such as the MSX often had a special labeled "dead key", which in combination with the Ctrl and Shift keys could add the accents "´", "`", "ˆ" and "¨" to vowels that were typed subsequently.

Caps Lock is a dead key, however Ctrl and Shift aren't, since they have to be held down to use.

• Compose key
• Microsoft's Keyboard shortcuts for international characters