Positional faithfulness, positional neutralisation and Shona vowel harmony

The distribution of the feature [high] in Shona verbs is a prototypical example of positional neutralisation accompanied by vowel harmony. In languages which exhibit positional neutralisation of vowel contrasts, one or more vowels (generally, the most marked members of the vowel inventory) may occur distinctively in only a small subset of the structural positions available in the language. Outside of these positions, the marked vowels may surface only if they harmonise with a similar vowel in the privileged position. For example, the mid vowels e and o in Shona verbs are contrastive only in root-initial syllables. These vowels may appear in subsequent syllables only when preceded by a mid vowel in root-initial position. A string of height-harmonic Shona vowels is therefore firmly anchored in the root-initial syllable, as shown in (1):