An opposition of two vowels of the same degree of aperture is not present as long as a corresponding vocalic opposition of a narrower degree of aperture is lacking.
Standardized
IF there is an opposition of two vowels of the same aperture, THEN there is a corresponding vocalic opposition of a narrower degree of aperture.
1. Explicitly stated as a universal acquisitional sequence, but can be assumed to be intended also as a universal implication.2. See discussion in Hawkins (1987).
1. Explicitly stated as a universal acquisitional sequence, but can be assumed to be intended also as a universal implication.2. See discussion in Hawkins (1987).