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In phonology and phonetics, raising is a sound change in which a vowel or consonant becomes higher or raised, meaning that the tongue becomes more elevated or positioned closer to the roof of the mouth than before. The opposite effect is known as lowering. Raising or lowering may be triggered by a nearby sound, in which case they are a form of assimilation, or they may occur on their own.
In i-mutation, a front vowel is raised before /i/ or /j/. This is assimilation.
In the Attic dialect of Ancient Greek and in Koine Greek, close-mid /e: o:/ were raised to /i: u:/. This change occurred in all cases and was not triggered by a nearby front consonant or vowel. Later, Ancient Greek /?:/ was raised to become Koine Greek [e:] and then [i:]. For more information, see Ancient Greek phonology § Vowel raising and fronting
In Czech, the alveolar trill /r/ was raised before /i/ to become the raised alveolar trill , spelled ⟨?⟩ as in ⟨Dvo?ák⟩. This is a form of palatalization, and it also occurred in Polish, where it became a simple sibilant fricative /?/ (spelled ⟨rz⟩ or ⟨?⟩) around the 16th century. The pronunciation is considered to be non-standard, and is used only by some older speakers.