Universal 685:

Original: All languages have the place distinctions of high and low and of front and back in their vowel systems; hence vowel systems minimally include /i, a, u/.
Standardized: All languages have the place distinctions of high and low and of front and back in their vowel systems; hence vowel systems minimally include /i, a, u/.
Keywords: vowel, high, low, front, back
Domain: phonology
Type: unconditional
Status: achronic
Quality: almost absolute
Basis: sample of 209 languages in Crothers 1978
Source: Crothers 1978, cited in Holenstein 1985: 124

Counterexamples: Some Caucasian languages have only two vowel phonemes, with the single place distinction being high and low.

FP