Given a word class W of lexical items which inflect for a morphological category C, given the set of values V that C assumes, and given the morphemes representing V with their allomorphs, then an inflection class is a subclass of W defined by the set of allomorphs that it takes in inflecting for C. For instance, English verbs fall into the conjugation classes of weak and strong verbs by the criterion of whether they form the past tense by the suffix -ed or in some other way; and the strong class again has subclasses according to the kind of morphological modification applied in the formation of the past tense and the perfect participle.