The most important "silent" letter is the "mute e". In spoken French today, final "e" is, in some regional accents (in Paris for example), omitted after consonants; but in Classical French prosody, it was considered an integral part of the rhyme even when following the vowel. "Joue" could rhyme with "boue", but not with "trou". Rhyming words ending with this silent "e" were said to make up a "double rhyme", while words not ending with this silent "e" made up a "single rhyme". It was a principle of stanza-formation that single and double rhymes had to alternate in the stanza. Virtually all 17th-century French plays in verse alternate masculine and feminine couplets.