Vowel harmony

In linguistics, a language exhibiting vowel harmony has a phonological rule that requires all vowels in a word to belong to a single class of vowels. The most common types of vowel harmony rules are rules requiring all vowels to be either rounded or unrounded, or requiring all vowels to be either front or back vowels.

For example, in the Finnish language, there are three classes of vowels:

Front vowels: (/ü/, /ö/, /æ/)
Back vowels: (/u/, /o/, /a/)
Neutral vowels: (/i/, /e/) [non-low unrounded vowels]

And the rule states that words may contain vowels from group 3 and/or vowels from either group 1 or group 2 (but not both 1 and 2). Thus, [tütö], [tütöti], and [tutoti] are permissible, but *[tutöti] and *[tüto] are not.

As a consequence Finns often have trouble pronouncing foreign loanwords which violate these rules. The word "Olympia" for example, tends to become "Olumpia" in their mouths.

In Mongolian, the rule states:

Front vowels: (/e/, /�/, /�/)
Back vowels: (/a/, /o/, /u/)
Neutral vowel: (/i/)

Other languages, such as Middle Korean, have more arbitrary class-membership rules. (Modern Korean does not exhibit vowel harmony.)

This phenomenon has been documented in Telugu, several Bantu languages, and almost all languages in the Ural-Altaic language family.

Compound words often violate this rule; for instance the Finnish month name "syyskuu" ("kuu" means month). In such words suffixes agree with the vowels in the last part: syyskuuta.

The counterpart of vowel harmony, consonant harmony, is less widespread. Most commonly, consonant harmony requires all the sibilants of the word to belong either to the anterior class (s-like sounds) or the nonanterior class (sh-like sounds). Such patterns are found in Navajo, Kinyarwanda, and elsewhere. Various Austronesian languages exhibit consonant harmony among the liquids, with [r] assimilating at a distance to [l] or vice versa.