French exhibits perhaps the most extensive phonetic changes (from Latin) of any of the Romance languages.
⟨au⟩ was retained, but various languages (including Old French) eventually turned it into /ɔ/ after the original /ɔ/ fell victim to further changes.
Modern French also had lost the class of rather unpredictable -ier verbs (resulting from ejection of /j/ into the infinitive suffix -āre, which still exists in some langues d'oïl), having been replaced by simple -er verbs plus ⟨-i⟩ instead, as in manier, but Old French laissier → laisser.
That especially applied to the new long vowels, many of which broke into diphthongs but with different results in each daughter language.
[citation needed] Old French underwent more thorough alterations of its sound system than did the other Romance languages.
In Old French, it went even further than in any other Romance language; of the seven vowels inherited from Vulgar Latin, only /i/ remained unchanged in stressed open syllables:[citation needed] Furthermore, all instances of Latin long ū > Proto-Romance /u/ became /y/, the lip-rounded sound that is written ⟨u⟩ in Modern French.
Old French shared with the rest of the Vulgar Latin world the loss of final ⟨-M⟩.
Old French also dropped many internal consonants when they followed the strongly stressed syllable; Latin petram > Proto-Romance */ˈpɛðra/ > OF pierre; cf.
The doublet of français and François in modern French orthography demonstrates the mix of dialectal features.
[citation needed] The following table shows the most important modern outcomes of Vulgar Latin vowels, starting from the seven-vowel system of Proto-Western Romance stressed syllables: /a/, /ɛ/, /e/, /i/, /ɔ/, /o/, /u/.
^3 However, the sequences */ueu/ from multiple origins regularly dissimilate to /jɛw/ (and later /jœ/, /jø/) except after labials and velars (Latin locus → /lueu/ → lieu /ljø/, but *volet → [vuoɫt] → [vueɫt] → [vueut] → veut /vø/).
[6] ^4 The changes producing French moitié /mwaˈtje/ were approximately as follows: Evidence of 9th century French phonology is relatively limited, being based largely on two short documents, the Oaths of Strasbourg, written in 842 in what was likely a deliberately Latinized, archaic form of Romance, and the Sequence of Saint Eulalia, written around 880 in some Romance vernacular of north central France,[15] not directly ancestral to modern French (the modern French form chose requires palatalization of /ka/ to have taken place before monophthongization of [au̯], whereas the Sequence's "cose" shows only the latter of these two sound changes, as in modern Picard[16]).