1.3.3. Speech acts

Although we have spoken easily of the truth value of an arbitrary sentence φ, there are some sentences that not only do not have truth values but cannot have them. It would be crazy to respond to a question like What time is it? by saying True enough or You’re wrong! And these responses would be equally out of place in the case of an imperative sentence like Please shut the door.

Questions and imperatives are clear cases of sentences where truth values do not matter. But they may be beside the point in the case of some declarative sentences. Saying True enough or You’re wrong! would be out of place in response to a sentence like I promise to be here tomorrow or I apologize for what I said but for somewhat different reasons than in the case of questions and commands. The verbs promise and apologize can be used to describe certain sorts of actions that can be performed using language. And, when they are used in the first person present tense (as in the sentences above) by the right person under the right circumstances, they can be used to perform the sort of actions they describe. That is, by saying I apologize for what I said, I can do something that can be described truly by the sentence He apologized for what he said. Verbs like this were labeled performative by J. L. Austin, the philosophy who did the most to call attention to the variety of speech acts.

Austin estimated that the performative verbs in English number on the order of the third power of 10. If this estimate is accurate, there are thousands of kinds of speech act besides assertion and thousands of varieties of force beyond the sort of force we will focus on. Much of this vocabulary does mark fairly subtle differences of force between speech acts, but the fact that we have vocabulary for making such subtle distinctions only indicates the importance to us of knowing the specific force that an utterance had. Moreover, we need not use performative verbs to perform that acts these verbs describe. I can apologize without saying I apologize and I can make a promise without saying I promise. So we can expect that many (perhaps even most) declarative sentences are not used to make assertions.

In spite of this, we will not consider speech acts other than assertion, and our interest in assertion itself will be limited to one aspect of its force: the expression of a proposition. Although this will cut us off from much of the richness of language, it will not cut us off from much that is central to deductive reasoning. Of course, there is a sense in which conclusions can be drawn from apologies and promises, but such inferences will tend to be matched by conclusions drawn from ordinary assertions using performative verbs to describe apologies and promises (rather than make them). Moreover, many accounts of speech acts other than assertion treat propositions as important components of their meaning, and this gives the logic of assertions a central place in the logic of all speech acts.