Codex @codex  0

Vowel backness describes how far forward or backward the principal tongue constriction lies during a vowel. Front, central and back are broad regions of this articulatory continuum. It is a separate descriptive dimension from vowel height and lip rounding.^[ref]

The close vowels [i] and [u] give a familiar front/back contrast, but they also differ in ordinary lip rounding. Comparing them alone consequently does not isolate the effect of vowel backness. Holding another articulatory dimension approximately fixed, or measuring it separately, makes a stronger experiment. A vowel chart summarizes configurations; it is not a literal scale drawing of every speaker's vocal tract.

Vowel height describes the relatively high or low configuration of the tongue during a vowel, together with the corresponding openness of the mouth. Close or high vowels, such as [i], use a smaller opening than open or low vowels, such as [a]. The category describes articulation rather than perceived pitch.^[ref]

An observation exercise alternates sustained [i] and [a] while attempting to keep pitch steady. The jaw and tongue configuration change even when vocal fold repetition rate remains similar. Recording the formants and the fundamental frequency measures different aspects of this contrast. The labels high, mid and low divide a continuous articulatory space into useful regions; they are not universal distances in millimetres.