Complementary Distribution - in Morphology

In Morphology

The concept of complementary distribution is applied in the analysis of word forms (morphology). Two different word forms (allomorphs) can actually be different "faces" of one and the same word (morpheme). For example, consider the English indefinite articles a and an. The usages an aardvark and a bear are grammatical. But the usages *a aardvark and *an bear are ungrammatical (marked with "*" in linguistics).

The form an is used "in the environment" before a word beginning with a vowel sound.

This linguistic environment can be notated as "__ V".

The form a is used in the environment before a word beginning with a consonant sound.

This can be notated as "__ C".

The "distribution" (usage according to environments) of the forms an and a is "complementary" because of three factors ---

(1) an is used where a is not used;

(2) a is used where an is not used;

(3) when you take the environment where an is used, and the environment where a is used, the two environments together cover every legitimate potential environment for the word.

The forms an and a function to work together like a team, in order to take care of every instance (environment) where the English indefinite article is needed. This is why we say that they are two different "forms" of the same "word", instead of saying that they are "two different words".