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.
In morphology, two morphemes are in contrastive distribution if they occur in the same environment, but have different meanings.
They are both used to indicate nominative case, and their occurrence is conditioned by the final sound of the preceding noun.
/-(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.
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.