死键

What is a Dead Key?

A dead key is a keyboard key that does not produce a character immediately when pressed — instead, it waits for the next keystroke and combines the two inputs to produce a modified character. The key is "dead" because pressing it alone produces nothing visible; it only comes alive when followed by a compatible base character.

Dead keys are the primary mechanism for typing accented characters on keyboards that don't have dedicated keys for every diacritic combination. They are ubiquitous on European keyboard layouts: the French AZERTY keyboard has dead keys for ^ and ¨, the German QWERTZ keyboard has dead keys for ^ and ´, and many others.

How Dead Keys Work

1. Press the dead key (e.g., the key labeled ´ acute accent)
2. The cursor shows nothing (or a placeholder like ´ underlined in some implementations)
3. Press a base character (e.g., e)
4. The combined character is output (é)

If the combination is not defined, most systems either output both characters separately (´ then e) or just the dead key's nominal character.

Common Dead Keys and Their Combinations

To type the dead key's character alone (e.g., just an acute ´ as a standalone diacritic), press the dead key followed by Space. This produces the standalone combining or spacing diacritic.

Dead Keys on macOS

macOS uses the Option key as a dead key modifier in the US keyboard layout:

So: Option + e, then e = é. Option + u, then u = ü. The long-press character popover (introduced in macOS Lion) provides an even simpler alternative.

Dead Keys vs. Compose Keys

Unicode Encoding

Dead key combinations produce precomposed Unicode characters (e.g., é = U+00E9), not a base character followed by a combining mark. The IME/keyboard driver performs this composition and outputs the single code point. If no precomposed form exists, some systems fall back to the base + combining mark representation.

Quick Facts