想像可能な命題とはどのような命題であるか？

抄録

We can imagine innumerable propositions, including ones that are not actually true. But not all propositions are imaginable. We have difficulty in imagining some propositions, such as logically contradictory or conceptually incoherent ones. So what kinds of propositions are imaginable? How can we characterize imaginable propositions?
One possible answer is what we might call the Humean Hypothesis, according to which p is imaginable if and only if p is possible. But there are some serious counterexamples to the Humean Hypothesis. For instance, the proposition that Hesperus is not Phosphorus is clearly imaginable, but it is not possible. A better answer is provided by the Same Possible Content Hypothesis, which says that p is imaginable if and only if p is believable. The Same Possible Content Hypothesis is so called, because it says that the possible propositional content of the imagination coincides with the possible propositional content of belief. This hypothesis seems to be plausible, and it is free from the difficulties that the Humean Hypothesis faces. The proposition that Hesperus is not Phosphorus is imaginable and, at the same time, it is also believable.
The Same Possible Content Hypothesis offers a way to investigate the nature of the mental state of imagination. Some philosophers have pointed out the similarity between imagination and belief, especially in terms of inferential coherence, triggering emotion and causing behavior. And the Same Possible Content Hypothesis adds further weight to their claim, revealing a new aspect in which imagination and belief are similar. By investigating the underlying causes of these similarities, we will be able to learn more about the nature of imagination and belief.