Presupposition is surely one of the most debated notions in the linguistic and philosophical literature. Historically, there are two main theoretical approaches to presuppositions. According to the first one, the semantic view, presuppositions are semantic implications, that is, truth-conditional relations between propositions and statements. In this sense, presuppositions are considered properties of sentences and a presupposed proposition is a necessary condition for the truth of the presupposing statement. In the second approach, the pragmatic view, presuppositions are not properties of sentences but rather properties of speakers or of linguistic performances given a certain context of utterance. From this view, a presupposed proposition is a condition for the felicitous utterance of the presupposing statement in a given context.

Traditionally, it is assumed that semantic presuppositions differ from classical entailments, as presuppositions, unlike classical entailments, project under negation: if we compare a context of entailment to a context of presupposition, we should see that entailments, but not presuppositions, disappear under negation. This presentation aims to propose a revision of the semantic notion of presupposition. I argue that most standard cases of presuppositions are classical entailments. Moreover, I claim that all presuppositions that are classical entailments are also pragmatic presuppositions, while not all pragmatic presuppositions are also classical entailments. I contend that factive verbs offer a paradigmatic example of this distinction, as the factivity related to know is semantic, hence a classical entailment, whereas the factivity related to regret is merely pragmatic. This claim stands in contrast to Karttunen’s (1971) well-known analysis of factive verbs and his distinction between true factives (that is, emotive factives) and semifactives (that is, cognitive factives).

In linguistics and in the philosophy of language it is standardly assumed that know is a factive verb, meaning that a sentence such as X knows that p, when uttered in its positive declarative form, presupposes, in fact entails, the truth of its complement. A problem for this analysis is the fact that the verb know can be used non-factively in contexts where it is evident that the proposition expressed by the subordinate clause is not true. In order to account for non-factive uses of know, two main solutions have been advanced in the literature. Hazlett (2009, 2010, 2012) proposes that know is not semantically factive and a sentence such as X knows that p does not entail, but only pragmatically implies p. On the other hand, Tsohatzidis (2012) argues that know is lexically ambiguous between a factive and a non-factive sense: when know is used in its factive sense, a sentence such as X knows that p entails p, whereas, when know occurs in its non-factive sense, it does not.

As shown in recent works by Colonna Dahlman (2015, 2016, 2017b), the phenomenon at issue―the possibility for a speaker to use know in cases where the proposition expressed by the clause embedded under ‘knows’ is not true―is not unique to English, but occurs, for instance, also in Italian. We carried out a Truth Judgment Task to test the hypothesis that the Italian lexical item ‘sa’ (‘knows’) is ambiguous. Our findings are consistent with the lexical ambiguity hypothesis, and cannot be explained by Hazlett’s pragmatic solution.