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.