K. assumes that there is a distinction between the semantic representation of a sentence, consisting of a proposition and a number of presuppositions, and the set of implications derivable from it by general rules of inference. He argues that there are at least seven classes of verbs taking complement sentences: factives (e.g. 'realize'), counterfactives (e.g. 'pretend'), implicative verbs (e.g. 'manage'), negative implicatives (e.g. 'fail'), only-if verbs (e.g. 'be able'), if-verbs (e.g. 'force'), negative if-verbs (e.g. 'prevent').