Vowel hiatus

Vowel hiatus occurs when two vowel sounds are made in adjacent syllables with no intervening consonant sound.

English phonotactics strongly disfavours hiatus. It only really occurs with a final schwa sound after a previous vowel, e.g. as in non-rhotic fire /faɪ.ə/. It also really occurs in anything with the ɴᴇᴀʀ vowel phoneme that lacks a following R or L.

Otherwise, hiatus is generally avoided by:

• Use of the indefinite article an rather than a, e.g. an apple rather than *a apple.
• Use of linking sounds, i.e. linking /r/, linking /j/ and linking /w/.

Speakers with rhotic accents may permit vowel hiatus where there is no R, to avoid linking /r/. Speakers with non‑rhotic accents tend to use intrusive /r/ to avoid hiatus in this situation.

Vowel hiatus is also avoided in some other languages, particularly French.

Contrast diphthong (when two vowels occur together in the same syllable).