Contrastive distribution


Contrastive distribution in linguistics, as opposed to complementary distribution or free variation, is the relationship between two different elements in which both elements are found in the same environment with a change in meaning.

Phonology

In phonology, two sounds of a language are said to be in contrastive distribution if replacing one with the other in the same phonological environment results in a change in meaning. If a sound is in contrastive distribution, it is considered a phoneme in that language.
For example, in English, the sounds and can both occur word-initially, as in the words pat and bat, which are distinct morphemes. Therefore, and are in contrastive distribution and so are phonemes of English.
Note that two sounds that are in contrastive distribution in one language can be in complementary distribution or free variation in another. These sounds occur in English, as in the word team and steam, but their occurrence is purely dependent upon phonological context. Therefore, in English, and are not in contrastive distribution but in complementary distribution.

Morphology

In morphology, two morphemes are in contrastive distribution if they occur in the same environment, but have different meanings.
For example, in Korean, noun phrases are followed by one of the various markers that indicate syntactic role: /-ka/, /-i/, /-ul/, etc. /-ka/ and /-i/ are in complementary distribution. They are both used to indicate nominative case, and their occurrence is conditioned by the final sound of the preceding noun. If the noun ends in a consonant, /-i/ occurs; otherwise, /-ka/. /-ul/, on the other hand, occurs in the same position as /-i/ or /-ka/ and is also conditioned by the immediately previous sound, but it indicates the accusative case. Therefore, /-ul/ and the set are in contrastive distribution.

Syntax

In syntax, the requirements are similar. In English, the expression of the indicative and the subjunctive moods is contrastive:
The change from non-past first-person singular indicative am to the subjunctive were results in a change in the grammatical mood of the sentence.