Some linguists propose the Ural-Altaic grouping of the Altaic languages (Turkish, Mongolian, Kazakh, Uzbek, Tatar, Manchu, etc., plus perhaps Korean and Japanese) and Uralic languages (Hungarian, Finnish and Estonian mostly) into one language group. Cases can be made both for and against this. Both groups follow the principle of vowel harmony, are agglutinative (stringing suffixes, prefixes or both onto a single root) and lack any way for expressing grammatical gender (see noun case). However, the vocabulary of both groups does not correspond, except for borrowings. Thus it remains for the linguists of the future to prove or disprove this proposal.