Synérèse is the metrical operation inverse to diérèse, collapsing two potential vowel sounds into a single syllable for the purposes of versification. It reflects the natural tendency of spoken French to reduce vowel sequences, and in poetry it allows the poet to accommodate a word to a metrical pattern that would otherwise be disrupted by a full two-syllable pronunciation. The systematic management of synérèse and diérèse in classical French poetry is one of its most distinctive technical features, requiring poets to make deliberate choices about pronunciation that differ from ordinary speech, revealing the extent to which classical verse constitutes a separate, formal version of the language.

Synérèse affects how adjacent vowels are counted in French verse by merging them into a single syllabic unit rather than separating them. Students must distinguish synérèse carefully from diérèse, since this directly changes metrical analysis. Pronunciation conventions vary historically, so scansion requires contextual sensitivity rather than rigid modern assumptions. Understanding synérèse is essential for reading classical French verse accurately, where syllable count determines formal structure and interpretive rhythm.