Latin

====Diphthongs====
Classical Latin had several [[diphthong]]s. The two most common were {{angbr|ae au}}. {{angbr|oe}} was fairly rare, and {{angbr|ui eu ei}} were very rare, at least in native Latin words.<ref name="classical diphthongs">{{Harvnb|Allen|1978|pp=60–63}}</ref> There has also been debate over whether {{angbr|ui}} is truly a diphthong in Classical Latin, due to its rarity, absence in works of Roman grammarians, and the roots of Classical Latin words (i.e. {{lang|la|hui ce}} to {{lang|la|huic}}, {{lang|la|quoi}} to {{lang|la|cui}}, etc.) not matching or being similar to the pronunciation of classical words if {{angbr|ui}} were to be considered a diphthong.<ref>{{cite journal|jstor=282713|title=The Diphthong -ui in Latin|journal=Transactions and Proceedings of the American Philological Association|volume=41|pages=19–23|last=Husband|first=Richard|date=1910|doi=10.2307/282713}}{{cbignore|bot=medic}}</ref>

The sequences sometimes did not represent diphthongs. {{angbr|ae}} and {{angbr|oe}} also represented a sequence of two vowels in different syllables in {{lang|la|aēnus}} {{IPA|[aˈeː.nʊs]}} "of bronze" and {{lang|la|coēpit}} {{IPA|[kɔˈeː.pɪt]}} "began", and {{angbr|au ui eu ei ou}} represented sequences of two vowels or of a vowel and one of the semivowels {{IPA|/j w/}}, in {{lang|la|cavē}} {{IPA|[ˈka.weː]}} "beware!", {{lang|la|cuius}} {{IPA|[ˈkʊj.jʊs]}} "whose", {{lang|la|monuī}} {{IPA|[ˈmɔn.ʊ.iː]}} "I warned", {{lang|la|solvī}} {{IPA|[ˈsɔɫ.wiː]}} "I released", {{lang|la|dēlēvī}} {{IPA|[deːˈleː.wiː]}} "I destroyed", {{lang|la|eius}} {{IPA|[ˈɛj.jʊs]}} "his", and {{lang|la|novus}} {{IPA|[ˈnɔ.wʊs]}} "new".

Old Latin had more diphthongs, but most of them changed into long vowels in Classical Latin. The Old Latin diphthong {{angbr|ai}} and the sequence {{angbr|āī}} became Classical {{angbr|ae}}. Old Latin {{angbr|oi}} and {{angbr|ou}} changed to Classical {{angbr|ū}}, except in a few words whose {{angbr|oi}} became Classical {{angbr|oe}}. These two developments sometimes occurred in different words from the same root: for instance, Classical {{lang|la|poena}} "punishment" and {{lang|la|pūnīre}} "to punish".<ref name="classical diphthongs" /> Early Old Latin {{angbr|ei}} usually monophthongized to a later Old Latin {{angbr|ē}}, to Classical {{angbr|ī}}.<ref>{{Harvnb|Allen|1978|pp=53–55}}</ref>

By the late Roman Empire, {{angbr|ae oe}} had merged with {{angbr|e ē}}. During the Classical period this sound change was present in some rural dialects, but deliberately avoided by well-educated speakers.<ref name="classical diphthongs" />

{| class="wikitable" style="text-align: center;"
|+ Diphthongs classified by beginning sound
! !! Front !! Back
|-
! Close
| || ui {{IPA|/ui̯/}}
|-
! Mid
| ei {{IPA|/ei̯/}}<br />eu {{IPA|/eu̯/}} || oe {{IPA|/oe̯/}}<br />ou {{IPA|/ou̯/}}
|-
! Open
| colspan="2" | ae {{IPA|/ae̯/}}<br />au {{IPA|/au̯/}}
|}