What is complementary distribution?

• A. Two sounds co-occur freely in the same environment.
• B. A relationship where two sounds are never found in the same phonetic environment; their allophones occur in mutually exclusive contexts.
• C. A phoneme that changes meaning in different contexts.
• D. A type of accent feature.

Answer: (B)

Complementary distribution means two sounds never appear in the same phonetic environment because they are allophones of the same underlying phoneme. Their use depends on the context, and the two realizations occupy mutually exclusive environments.

A classic example is the English stops/p-less aspirated vs unaspirated. The sound pair for /p/ is realized as [pʰ] in syllable-initial positions like in “pin,” but as [p] after an initial /s/ in a cluster like in “spin.” These two realizations never occur in the same context, so they are just different surface forms of one underlying phoneme.

Because they are tied to context rather than to different meanings, swapping one for the other does not change the word’s meaning. That’s what sets complementary distribution apart from a phoneme contrast, where different sounds do change meaning. It’s also not about free variation, where speakers might choose one allophone or another in the same context.

In sum, complementary distribution describes non-overlapping, context-driven realizations of the same phoneme.