Abstract

The thought experiment is a seemingly indispensable tool in the armchair philosopher’s toolbox. One wonders, for example, how philosophers could come to think that justified true belief isn’t knowledge, that reference isn’t determined by an expression’s associated description, or that moral responsibility doesn’t require the ability to do otherwise, without the use of thought experiments. But even if thought experiments play an integral role in philosophical methodology, their legitimacy is at least initially puzzling: one would think that significant knowledge of the world requires extensive empirical investigation. But since thought experiments are done from the armchair, how can they tell us about the world? A standard account of the nature and utility of thought experiments provides an answer to this question, and in a way that fits naturally with a standard picture of the nature of the facts philosophers investigate: Philosophers are about the business of investigating the essences of things and kinds. But a thing’s essential and accidental properties are modal properties. Thus, one can discern a thing’s essence by discovering its modal profile. But if so, then thought experiments are naturally suited as tools for the armchair philosopher. For thought experiments shed light on modal facts. Therefore, since philosophers investigate essences, facts about essence are modal facts, and the thought experiment is one of the few tools they have for discerning such facts, thought experiments play a legitimate and indispensable role in philosophical methodology. In my dissertation, I argue that the standard account of the nature and utility of thought experiments is inadequate, and sketch a more promising account. First, I argue that our knowledge of possibility is restricted to the relatively humdrum. And if so, then since the standard account ties the utility of thought experiments to our knowledge of possibility, too many thought experiments will be ruled out as useless, which raises serious concerns about the significance, and perhaps even the legitimacy, of armchair philosophy. Thus, there is pressure for armchair philosophers to reject the standard account. Second, I sketch an alternative picture of the nature of facts philosophers investigate – one that’s more fine-grained than the standard modal-profile picture. Relatedly, I sketch a correspondingly fine-grained semantics for claims about such facts. This alternative picture underwrites the legitimacy of a hitherto underappreciated sort of thought experiment, which I call the non-modal thought experiment. Such thought experiments shed light on facts about the world that are more fine-grained than what can be discerned by merely examining their modal profiles. I argue that non-modal thought experiments often succeed at just the points where the more familiar modal thought experiments fail, and thus that the two are naturally suited to complement one another in the philosopher’s practice. Finally, I exploit the points mentioned above to sketch an account of the variety and utility of thought experiments that’s much more nuanced than that of the standard account. I then illustrate some of its virtues by indicating its ability to account for a wide range of epistemically forceful thought experiments – both humdrum and exotic –, and by demonstrating how it can be used to make progress in debates that have reached a stalemate due to conflicting modal intuitions.