Based on Brandtler (2012), this paper argues that polarity items are sensitive to evaluability, a concept that refers to the possibility of accepting or rejecting an utterance as true in a communicative exchange. The main distinction is made between evaluable and non-evaluable utterances. The evaluable category comprises any clause that asserts, presupposes or entails the truth of an affirmative or a negative proposition. In contrast, the non-evaluable category contains clauses that do not assert, presuppose or entail the truth of an affirmative or a negative proposition.According to the Evaluability Hypothesis, non-evaluable environments are natural hosts for both NPIs and PPIs. Hence, the occurrence of polarity items in non-evaluable clauses does not require formal licensing, and this is the reason we find both PPIs and weak NPIs in yes/noquestions and conditionals. Evaluable clauses, in contrast, are restricted environments and may only host polarity items that are formally (i.e. syntactically) licensed. Hence, NPIs require the presence of a licensing element, and PPIs require the absence of such elements. This analysis leads to an important change of perspective, as the occurrence of polarity items in negative and affirmative sentences becomes the marked, or exceptional, case.