3.1: Truth as a guide to sentence meaning

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Any speaker of English will “understand” the simple sentence in (1), i.e., will know what it “means”. But what kind of knowledge does this involve? Can our hypothetical speaker tell us, for example, whether the sentence is true?

(1) King Henry VIII snores.

It turns out that a sentence by itself is neither true nor false: its truth value can only be determined relative to a specific situation (or state of affairs, or universe of discourse). In the real world at the time that I am writing this chapter (early in the 21^st century), the sentence is clearly false, because Henry VIII died in 1547 AD. The sentence may well have been true in, say, 1525 AD; but most speakers of English probably do not know whether or not it was in fact true, because we do not have total knowledge of the state of the world at that time.

So knowing the meaning of a sentence does not necessarily mean that we know whether or not it is true in a particular situation; but it does mean that we know the kinds of situations in which the sentence would be true. Sentence (1) will be true in any universe of discourse in which the individual named King Henry VIII has the property of snoring. We will adopt the common view of sentence meanings expressed in (2):

(2) “To know the meaning of a [declarative] sentence is to know what the world would have to be like for the sentence to be true.” (Dowty et al. 1981: 4)

The meaning of a simple declarative sentence is called a proposition. A proposition is a claim about the world which may (in general) be true in some situations and false in others. Some scholars hold that a sentence, as a grammatical entity, cannot have a truth value. Speakers speak truly when they use a sentence to perform a certain type of speech act, namely a statement (making a claim about the world), provided that the meaning (i.e., the sense) of the sentence corresponds to the situation about which the claim is being made. Under this view, when we speak of sentences as being true or false we are using a common but imprecise manner of speaking. It is the proposition expressed by the sentence, rather than the sentence itself, which can be true or false.

In §3.2 we will look at various types of propositions: some which must always be true, some which can never be true, and some (the “normal” case) which may be either true or false depending on the situation. In §3.3 we examine some important truth relations that can exist between pairs of propositions, of which perhaps the most important is the entailment relation. Entailment is a type of inference. We say that proposition p “entails” proposition q if p being true makes it certain that q is true as well. Finally, in §3.4, we introduce another type of inference known as a presupposition. Presupposition is a complex and controversial topic, but one which will be important in later chapters.