Streszczenie (autorskie):
Plain disjunctive sentences, such as The mystery box contains a blue ball or a yellow ball, typically imply that the speaker does not know which of the two disjuncts is true. This is known as an 'ignorance' inference. We can distinguish between two aspects of this inference: the negated universal upper bound part (i.e., the speaker is uncertain about each disjunct), which we call 'uncertainty', and the existential lower bound part (i.e., the speaker considers each disjunct possible), which we call 'possibility'. In the traditional approach, uncertainty is derived as an implicature, from which possibility follows. When disjunctions are embedded under a universal operator, such as It is certain that the mystery box contains a blue ball or a yellow ball, an inference analogous to possibility arises (i.e., it's possible that the mystery box contains a blue ball and it's possible that it contains a yellow ball). This inference is generally called a 'distributive' inference and the traditional approach derives it in the same way as in the unembedded case, from the corresponding negated universal inference (i.e. it is uncertain that the mystery box contains a blue ball and it is uncertain that it contains a yellow ball). In both the simple and the embedded cases, the traditional implicature approach predicts that the derived lower bound inference should never arise without the corresponding negated universal one. In this talk, we report on two experiments using a sentence-picture verification task based on the mystery box paradigm, the results of which challenge the traditional approach to ignorance and distributive inferences. Our findings show that possibility can arise without uncertainty, and that, in the same way, the distributive inference can arise without the corresponding negated universal one, thus calling for a reevaluation of the traditional view of disjunction and its inferences. We discuss how alternative theories can account for the observed patterns of inference derivation in a unified fashion and the open challenges that remain.