 It is natural to infer from both (52a) and (52b) that Barney has a sister and that he believes that he has a sister, and these inferences can be blocked in sentences such as those in (52c) and (52d) , where “his sister” occurs in the consequent of a conditional whose antecedent makes one or the other inference explicit. It may seem odd at first that (52c) should block the inference that Barney believes that he has a sister, while (52d) blocks the inference that Barney has a sister. Note however that, generally speaking, Barney has a sister iff he believes that he has a sister. We’ll return to this theme below.