 Vowels within a word "harmonize" to be either all front or all back.In particular, no native noncompound word can contain vowels from the group {"a", "o", "u"} together with vowels from the group {"ä", "ö", "y"}.Vowel harmony affects inflectional suffixes and derivational suffixes, which have two forms, one for use with back vowels, and the other with front vowels.