Vowel reduction (phonology)

In phonology, vowel reduction refers to changes in the number of vowels during the evolution of a language or across genetically related languages.

For example, the Russian language had lost the sound that corresponded to the letter Yat. For a long time the letter was pronounced exactly like the letter E, until it was removed from the Russian alphabet during the orthography reform of 1917.

An example of cross-language vowel reduction is provided by Japonic languages. Proto-Japanese had 8 vowels; this has been reduced to 5 in modern Japanese language, but in Yaeyama language the vowel reduction has progressed further, to 3 vowels.