features like [past] are provided with phonological material is called Vocabulary Insertion. In the case of Irregular verbs, the choice of affix, either -O or -t, is determined by the identity of the verb. That is, the affixes -O and -t, for e.g. hit hit-O and bend ben-t, are each specified for a list of the verbs on which they will appear. The insertion of the particular affixes -ed, -t, -O follows the Pān. inian principle, such that affixes with more specific conditions on insertion take precedence over less-specified affixes. Thus if the -O or -t affixes, which require specific lists for insertion, appear, the default past tense -ed will be blocked. From one point of view, the morphologist’s job is over when the list of stems to which restricted affixes apply have been identified. If these stems do not belong to a conjugational class, i.e., if this list is not relevant for the choice of other affixes, then the list is morphologically uninteresting. However, to say that the list is arbitrary is not to say that it does not have a structure that is important for both language acquisition and language use. Apparently, these lists are organized at least The status of Tense as a syntactic component separate from the Verb in English stems from Chomsky (1957). For discussion of the former issue, and clarification of a number of questions concerning the acquisition of such lists,