GENERAL: Two elements a and b are in complementary distribution if a, but not b, occurs in those
environments where on general grounds we may expect both a and b, while b, but not a
occurs in the complementary set of environments.
PHONOLOGY: Complementary distribution is often taken as an indication that two
superficially different elements are one and the same at a deeper level. Two sounds
/a/ and /b/ are in complementary distribution when one of the two (/a/) occurs in all
environments except those in which /b/ occurs and vice versa.
EXAMPLE: in English [p] and [ph] are in complementary distribution, since
[ph] occurs syllable-initially when it is directly followed by a stressed vowel
(cf. pin [phin]), whereas in all other positions [p] is found. In Hindi,
however, [p] and [ph] can occur in the same position and are distinctive.