Abstract

Contemporary analytic philosophy often relies on using conceivability as a guide to possibility. My dissertation addresses the question of whether conceivability is a legitimate guide to possibility. ;In order to understand this method, we need a metaphysics of modality. I defend Aristotelian actualism, the view that only actual entities exist; and what is possible or necessary depends on the actual world, and what might have been possible or necessary depends on what would have been actual had things gone differently. I defend several consequences of this view against Platonism and conventionalism. First, properties, propositions, and possible worlds are dependent on or contingent upon actuality. Second, the accessibility relation among Possible worlds is neither transitive nor symmetric, so T is the strongest valid modal logic. Third, merely possible worlds do not exist; possible worlds should be thought of as heuristic devices, not reifications of what might have been. Fourth, metaphysical or real modality is distinct from logical modality. ;With an Aristotelian actualist metaphysics of modality, I turn to the epistemology of possible worlds. Aristotelian actualism, makes our knowledge of modal truths far less puzzling than its rivals. Our knowledge of modality comes in part from a priori principles of possibility. Modal truths are rooted in the essences of actual things, so our knowledge of modal truths is rooted in our knowledge of actual truths. I defend this claim by explaining why essence and necessity are distinct. ;The Aristotelian actualist's metaphysics and epistemology provide the basis for investigating the relationship between conceivability and possibility. We attain knowledge of the possible via three tools: empirical facts about the actual world, a priori principles of possibility, and conceivability. In most interesting philosophical cases, we do not yet know the relevant principle of possibility. Here, we use a dialectic that involves what we can conceive. This kind of conceivability is fallible, and hence we must use caution