The results of vowel contraction were complex from dialect to dialect. Such contractions occur in the inflection of a number of different noun and verb classes and are among the most difficult aspects of Ancient Greek grammar. They were particularly important in the large class of "contracted verbs", denominative verbs formed from nouns and adjectives ending in a vowel. (In fact, the reflex of contracted verbs in Modern Greek, the set of verbs derived from Ancient Greek contracted verbs, represents one of the two main classes of verbs in that language.)