Contrastive distribution

A contrastive distribution in linguistics is a relationship between two or more different elements which can appear in the same context, but cause a change in meaning when one is substituted for another in that context. A contrastive distribution is demonstrated with a minimal pair.

Contrastive distribution is distinct from complementary distribution (when two elements cannot be substituted for one another) and free variation (where speech sounds can be substituted without changing the 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. The existence of a contrastive distribution between two speech sound plays an important role in establishing that they belong to two separate phonemes in a given language.

For example, in English, the speech sounds and  can both occur at the beginning of a word, as in the words pat and bat. Since and  both occur in the same phonological environment (i.e. at the beginning of a word) but change the meaning of the word they form, they are in contrastive distribution and therefore provide evidence for them being belonging to phonemes.

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/, /-(l)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/. /-(l)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, /-(l)ul/ and the set {/-i/, /-ka/} are in contrastive distribution.

Syntax
In syntax, the requirements are similar. In English, the expression of the indicative and the subjunctive moods is contrastive:


 * (1) If I am a rich man, then I have a lot of money.
 * (2) If I were a rich man, then I would have a lot of money.

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.