Accent in conjugation of reir

Question

Why is the i accented in the conjugation of reir but not in other e>i verbs? What is the rule for use of the accent here?

Silvia Piriz · Accepted Answer

Hola Bob M.
Great question! The accent on the í in reír (and its conjugations, e.g. ríe, ríen, riendo) is used to keep the stress on the correct syllable and to separate the two vowels so that they are pronounced in different syllables.
Without the accent, the two vowels e and i would normally form a diphthong (a single combined sound), but in reír, they must be pronounced separately: re-ír.
That’s why reír and similar verbs (sonreír, freír) need the written accent, whereas other e→i stem-changing verbs like servir or competir don’t — those don’t have two vowels together that could form a diphthong.
Saludos
Silvia