Abstract

Thought experiments are usually employed by philosophers as a tool in conceptual analysis. We pose ourselves questions such as “Would it be the same F if p?” or “Would it count as knowledge if q,” where p and q state some bizarre circumstances that are unlikely actually to occur and may even be beyond current technical possibility. The answers we are inclined to give to such questions are held to throw light on the nature of our concepts of, in these cases, identity and knowledge. But the facts about our concepts that are unearthed in this way are implicitly assumed to be deep, not superficial, facts. They are not meant to be facts contingent upon our current linguistic usage, psychology, or social structure, where these could easily be otherwise. If they were just facts of this superficial kind, it would hardly be worth the effort of uncovering them, for they would bind no-one who preferred a different convention or practice. The conceptual truths revealed are meant to be unavoidable, in some sense, and not merely conventional: there is something Platonic or Kantian in the background. The argument of Sections 2–8 of this essay is that, in the case of the thought experiments used to throw light on our concepts of person and personal identity, the results do not seem to be deep or hard to revise, and that this is so largely because of the ontological assumptions shared by more or less all participants in the debate. I shall be arguing that it is primarily these ontological assumptions, rather than the insight into our concepts that the thought experiments are supposed to bring, that determine the answers to the questions about persons and their identity. In the final two sections I shall make some cautious qualifications to this conclusion.