Modal illusions: Making sense of the necessary a posterior

A modal illusion is an illusion about what is and is not possible. Certain things seem like they could have been otherwise and other things seem like they could not have been otherwise. But sometimes these seemings are wrong. Specifically, there are certain necessary truths known a posteriori that seem to be merely contingently true. I maintain that this is most often due to the fact that while these truths are necessary, their negations are possible in another sense. Others argue that modal illusions are due to some other phenomenon, and in particular, that a person under a modal illusion does not imagine some impossible situation and mistakenly think that it is possible. By examining other accounts of modal illusions, I explain and explore the work that has been done in the area and argue against accounts that maintain that a person cannot and does not mistakenly think that an impossibility is possible when she is under a modal illusion.;The main examples I discuss first appeared in Saul Kripke's Naming and Necessity. Kripke's examples of the necessary a posteriori will often appear contingent and so a person might think that things could have been otherwise. For example, a person who thinks that water could have been something other than H2O is under a modal illusion. I group together explanations of these errors based on the assumptions that each type of account accepts or rejects.;In chapter 1, I explain different accounts of modal illusions and discuss the different theses each type of account is committed to. I also examine the consequences of holding these different accounts with regards to the overlapping area of philosophy of mind. Many have used examples of the necessary a posteriori to argue for dualism. I discuss the different ways a philosopher might use an explanation of modal illusions of the necessary a posteriori to argue for or against dualism.;In chapter 2, I examine and argue against the type of account that stems from a two-dimensional semantic framework, what I call a Two-Dimensionalist Account. Such an account holds that when a person is under a modal illusion, she does not think of some impossible situation and mistakenly think of it that it is possible. Instead, she imagines a world that would verify the sentence. She uses a sentence to midescribe the possibility. I hold that the Two-Dimensionalist Account is incorrect because it cannot be extended to treat more complicated occurrences of modal illusions, because it treats beliefs in a way that is very different than the way we normally treat beliefs, and because holding the two-dimensional semantic framework involves a radical departure from standard semantic theory.;In chapter 3, I examine and argue against the explanation offered by what I call Similarity Accounts, Kripke's own explanation being the primary example. Similarity Accounts also argue that a person subject to a modal illusion does not imagine some impossible situation and mistakenly think of it that it is possible. Rather, the situation the person has in mind must be redescribed. Really, the person is thinking of some similar object or substance and what could have been true of it. My objections to these types of account are threefold. First, these accounts are non-uniform in their treatment of modal beliefs. That is, these types of accounts differ in how they treat false modal intuitions and beliefs from the way we normally treat true modal intuitions and beliefs. Second, these explanations do not treat false modal intuitions in the way we normally treat false non-modal intuitions. The objects of false modal beliefs are different than the objects of false non-modal beliefs. Third, the claim that a person does not or cannot imagine the impossible is unmotivated. It is more likely that a person made a mistake about what is genuinely possible then that she made a mistake about the contents of her own thought.;In chapter 4, I offer a positive account of modal illusions, similar to those offered by Scott Soames and Steven Yablo. I argue that typical cases of modal illusion about the necessary a posteriori are due to the fact that some impossibilities are epistemically possible. p is epistemically possible if one cannot know that p is false a priori. The epistemic possibility of the necessary falsehoods discussed here explain how a person might think that they are possible in a metaphysical sense. (Abstract shortened by UMI.).