This study investigates the role of minimal contrast in phonetics and phonology. Two sounds are minimally contrastive when they differ in just one property. The main findings are that (i) minimal contrast can influence phonetic effects and (ii) phonological processes may single out minimally contrastive elements. An experiment tests the influence of minimal length contrast on the phonetic voicing effect, a pattern by which vowels are longer before voiced than before voiceless obstruents, in Lithuanian. In Lithuanian, only high and low vowels are minimally contrastive for length. The results indicate the voicing effect is more limited for those vowels that are minimally contrastive for length, showing a phonetic pattern sensitive to minimal contrast. Therefore, it is argued that the phonological representation must include information about minimal contrast. Minimal contrast is formalized with a contrast-coindexing function, which applies to minimally contrastive segments capable of distinguishing pairs of words.

Contrast-coindexing predicts that minimal contrast might also be active in the phonology. Evidence for this comes from vowel height harmony in Lena Asturian, where only vowels minimally contrastive for height can trigger harmony. The typology of vowel harmony from several varieties related to Lena further supports the active role of minimal contrast.