Phonological history of French
French exhibits perhaps the most extensive phonetic changes (from Latin) of any of the Romance languages. Similar changes are seen in some of the northern Italian regional languages, such as Lombard or Ligurian. Most other Romance languages are significantly more conservative phonetically, with Spanish, Italian, and especially Sardinian showing the most conservatism, and Portuguese, Occitan, Catalan, and Romanian showing moderate conservatism. French also shows enormous phonetic changes between the Old French period and the modern language. Spelling, however, has barely changed, which accounts for the wide differences between current spelling and pronunciation. Some of the most  profound changes have been: Only some of the changes are reflected in the orthography, which generally corresponds to the pronunciation of c. 1100–1200 CE (the Old French period) rather than modern pronunciation. This page documents the phonological history of French from a relatively technical standpoint. See also History of French#Internal history for a less technical introduction. Overview. A profound change in very late spoken Latin (Vulgar Latin, the forerunner of all the Romance languages) was the restructuring of the vowel system of Classical Latin. Latin had thirteen distinct vowels: ten pure vowels (long and short versions of a, e, i , o, u), and three diphthongs (ae, oe, au). What happened to Vulgar Latin is set forth in the table. Essentially, the ten pure vowels were reduced to the seven vowels , and vowel length was no longer a distinguishing feature. The diphthongs ae and oe fell in with and , respectively. Au was retained, but various languages (including Old French) eventually turned it into after the original fell victim to further changes. The complex but regular French sound changes have caused irregularities in the conjugation of Old French verbs, like stressed stems caused by historic diphthongization ("amer", aim, aimes", aime", aiment", but  amons, "amez"), or regular loss of certain phonemes ("vivre", "vif", vis", "vit"). Later in Modern French, these changes were limited to fewer irregular verbs. 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(resulting from ejection of /j/ into the infinitive suffix "-āre", which still exists in some "langues d'oïl"), having been replaced by simple "-er" verbs plus "-i" instead, as in "manier", but Old French "laissier" → "laisser". Vowel length became automatically determined by syllable structure, with stressed open syllables having long vowels and other syllables having short vowels. Furthermore, the stress on accented syllables became  more pronounced in Vulgar Latin than in Classical Latin. That tended to cause unaccented syllables to become less distinct, while working further changes on the sounds of the accented syllables. That especially applied to the new long vowels, many of which broke into diphthongs but with different results in each daughter language. Old French underwent thorougher alterations of its sound system than did the other Romance languages. Vowel breaking is observed to some extent in Spanish and Italian: Vulgar Latin focu(s) "fire" (in Classical Latin, "hearth") becomes Italian "fuoco" and Spanish "fuego". In Old French, it went even further than  in any other Romance language; of the seven vowels inherited from Vulgar Latin, only remained unchanged in stressed open syllables: Furthermore, all instances of Latin long ū > Proto-Romance became , the lip-rounded sound that is written "u" in Modern French. That occurred in both stressed and unstressed syllables, regardless of whether open or closed. Latin au did not share the fate of or ; Latin aurum > OF "or", "gold": not *"œur" nor *"our". Latin au must have been retained at the time such changes were affecting Proto-Romance. Changes affecting consonants were also quite pervasive in Old 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 > OF "pierre"; cf. Spanish "piedra" ("stone"). In some contexts, became , still written "oi" in Modern French. During the early Old French period, it was pronounced as the writing suggests, as as a falling diphthong: . It later shifted to become rising, , before becoming . The sound developed variously in different varieties of Oïl: most of the surviving languages maintain a pronunciation as , but Literary French adopted  a dialectal pronunciation, . The doublet of "français" and "François" in modern French orthography demonstrates the mix of dialectal features. At some point during the Old French period, vowels with a following nasal consonant began to be nasalized. While the process of losing the final nasal consonant took place after the Old French period, the nasal vowels that characterize Modern French appeared during the period in question. Table of vowel outcomes. 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: . The vowels developed differently in  different contexts, with the most important contexts being: Note that the developments in unstressed syllables were both simpler and less predictable. In Proto Western Romance there were only five vowels in unstressed syllables: , as low-mid vowels were raised to . These syllables were not subject to diphthongization and many of the other complex changes that affected stressed syllables. This produced many lexical and grammatical alternations between stressed and unstressed syllables. However, there was a strong tendency (especially beginning in the Middle French period, when the formerly strong stress accent was drastically weakened) to even out these alternations. In certain cases  in verbal paradigms an unstressed variant was imported into stressed syllables, but mostly it was the other way around, with the result that in Modern French all of the numerous vowels can appear in unstressed syllables. Changes that occurred due to contexts that developed during the Old French stage or later are indicated in the "Modern French" column. In particular, "+#" indicates a word-final context in modern French, which generally evolved due to loss of a final consonant in Old French or Middle French. For example, loss of in "aimé" "loved" (originally ) occurred in Old French, while loss of  in "sot" "silly" occurred in Middle French (hence its continuing presence in spelling, which tends to reflect later Old French). Chronological history. To Late Old French, c. 1250–1300. Changes here affect oral and nasal vowels alike, unless otherwise indicated. To Middle French, c. 1500. Changes here affect oral and nasal vowels alike, unless otherwise indicated. Nasalization. Progressive nasalization of vowels before or occurred over several hundred years, beginning with the low vowels, possibly as early as 900, and finished with the high vowels, possibly as late as c. 1300. Numerous changes occurred afterwards that are still continuing. The following steps  occurred during the Old French period: The following steps occurred during the Middle French period: The following steps occurred during the Modern French period: That leaves only four nasal vowels: , , , and , the last often no longer being distinguished from the first.