What is the relationship between the sentences in (1a) and (1b)?

At first glance, we might think that this is a simple case of entailment — if it is true that Zoe is looking after Noah’s dog, then it follows that Noah has a dog. But things are more complicated. Look at the sentence in (2a):

If we were dealing with entailment, (2a), which is a negation of (1a), should be compatible both with (1b) and with its negation (2b) — in entailment, if p is false, then q can be true or false. But instead, it seems that if (1a) is false, then (1b) must still be true. In other words, (1b) is true whether (1a) is true or false:

That Noah has a dog does not logically follow from sentences (1a) and (2a) at all. Instead, it is presupposed, i.e., presented as something that is taken for granted. The proposition associated with q is a presupposition of the proposition associated with p (we apologize for the terminology — now you have to distinguish prepositions, propositions and presuppositions).

But how is (1b) taken for granted? Do we take the existence of entities for granted simply by mentioning them? We do not, as the following examples show:

Example (3a) does not allow us to state whether Noah has a dog or not, and (3b) clearly allows us to state that he does not have a dog. Example (3c) even claims that the entity it mentions — bad dogs — do not exist at all.

Instead, there are specific linguistic phenomena that give rise to presuppositions (or “trigger” them, as philosophers say). Among these are definiteness (definite determiners, as in (4a), or possessives, like Noah’s dog) and proper names, as in (4b), all of which give rise to the presupposition that the entity referred to actually exists (this is called an existential presupposition):

Example (4a) shows that the existential presupposition is tied to the definite article: the sentence presupposes the existence of a dog, but not of a rabbit.

A second linguistic phenomenon that gives rise to presuppositions is the category of so-called factive verbs. Look at (5a) through (5d) and think about their relationship to (1b) (Noah has a dog):

Example (5a) presupposes (1b), while (5b) does not, and likewise, (5c) presupposes (1b) while (5d) does not — test this by negating the four sentences!

Verbs like know and regret are factive verbs, which means that they commit the speaker to the truth of the proposition expressed by the subordinate clause that follows, and this commitment remains even when they are negated. Other examples of factive verbs are discover, notice, realize, forget and care. In contrast, verbs like believe and report are non-factive, which means that they do not commit the speaker to the truth of the proposition expressed in the subordinate clause. Other examples of non-factive verbs are imagine, admit, claim, suggest, doubt and deny.

Other linguistic phenomena that trigger presuppositions are, for example, implicative verbs like manage or forget, aspectual verbs like start and stop, temporal subordinating conjunctions like before, after and since, and counterfactuals.

The presuppositions of a sentence remain constant not only when the proposition associated with that sentence is negated, but also when it is expressed as a question (as in (6a, b) or when it occurs in counterfactual sentences (as in 7a, b):

All four sentences presuppose that Noah has a dog, and both (6b) and (7b) additionally presuppose that Noah named his dog Laika.

However, while presuppositions remain constant whatever we do with a sentence, they can be cancelled by explicitly pointing out that they are false:

So, what happens to the truth of a sentence if its presuppositions are false? Philosophers of language generally agree that the truth value of such a sentence becomes indeterminate, i.e., it is neither true nor false. If Noah does not have a dog, then it is meaningless to ask whether it is true or false that Zoe watched Noah’s dog if he does not have a dog.

Linguists have a slightly different take, based on how speakers actually deal with situations where a presupposition of a sentence is false. Imagine that Zoe is falsely accused of spraying orange paint on a private airplane in order to protest against climate change. The lawyer of the airplane’s owner asks her the following:

According to the philosophers, Zoe would have to say something like (10a) or (10b), but in fact, she is more likely to say something like (10c):

In other words, we tend to treat sentences as false if their presuppositions are false, rather than treating them as meaningless. However, this is a pragmatic strategy — strictly speaking, the philosophers are right: you cannot not regret something that you have not done, not least because you would have to not regret an infinite number of things.

Expressive presuppositions

There is a special kind of presupposition that we have encountered before, even though we did not know it was a presupposition at the time. Recall the following sentence from Chapter 6, where we briefly discussed slurs:

We said at the time that the speaker of such a sentence is making two statements — the explicit one in (12a) and the implicit one in (12b):

We can now see that the proposition in (12b) is a presupposition — it remains constant if we negate (11), if we turn it into a question or if we embed it in a counterfactual context:

However, it is a special kind of presupposition in several ways: for example, it cannot be cancelled (see 14a), and the fact that it is false does not make the sentence indeterminate with respect to its truth value (see 14b):

This is because the presupposition does not concern some aspect of the world, but the attitude of the speaker. A better way of phrasing it would be (15):

The speaker demonstrates that that presupposition is true by using the slur, so it can never be false and hence it also cannot be cancelled.

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