Book excerpt: This book offers a new theory of the structure of propositions, which provides a uniform treatment of constative and performative sentences. Jerrold Katz shows that performatives can enter into logically valid arguments, even though, as Austin claimed, they can't be true or false. Katz also argues that âeoespeech act theoryâe is not a theory at all, but an assortment of observations about heterogeneous aspects of the performance of speech acts. He shows that a better explanation of speech acts is given by a grammatical account of the iIIocutionary potential of sentences and a separate pragmatic account of how this potential is realized in actual speech situtations. Katz provides such a grammatical account, which makes it possible for the first time to explain the iIIocutionary potential of sentences within grammar.