A distinction is to be drawn between a sentence including its meaning, on the one hand, and an utterance, on the other. An utterance is an occurrence of language activity, thus, eventually, part of a discourse. The expression occurrence implies an individual event of a certain species. Being a speech event, it means that all the variables represented by deictic expressions are replaced by constants. This includes importantly the speaker and the spatio-temporal coordinates of the speech event. Assume that is uttered by a witness in a particular law suit.

Then the reference of the definite NPs the defendant and the collision is fixed because these referents are established in the universe of discourse of that particular speech situation. Under such conditions, is either true or false (Strawson 1950).

Now eliminate all this knowledge and take just as a linguist's example sentence. Technically, it is then a system sentence (Lyons (1977:29-31), i.e. a sentence just representing the elements and rules of a particular language system irrespective of any linguistic or extralinguistic context that it might be used in. Then no particular defendent and no particular collision is being identified by . Consequently, the sentence has no truth value. A declarative sentence has a truth value only if the reference for all the referential expressions contained is fixed.