Some languages allow tense and lax vowels to contrast before word-final consonants but not word-finally, where only tense vowels are permitted. What is the motivation for this pattern? This paper proposes that the loss of vowel-duration contrasts in word-final positions is a phonetic precursor to word-final tensing. In languages where tense and lax vowels differ both spectrally and temporally, neutralization of duration contrasts in word-final positions results in tense-lax pairs differing only spectrally. If this spectral difference is not sufficient to support a phonemic contrast, the tense-lax contrast is neutralized altogether. The preference for tense vowels in case of neutralization can be explained as a preference for more distinct vowel contrasts in the F1xF2 space. Evidence for this account comes from an acoustic study of Swiss French showing that, although tense-lax contrasts are maintained both before word-final consonants and word-finally in this variety, they are signaled by temporal cues only before word-final consonants. While Dispersion-Theoretic analyses of vowel inventories tend to focus on F1 and F2, the present analysis suggests that distinctiveness along both spectral and temporal dimensions is relevant to understand the typology of phonological patterns
