Imagining as a Guide to Possibility

A great many arguments in philosophy turn on claims about what is possible, and in fact it’s difficult to overstate how central modal claims are in all areas of philosophy. Making claims about what could be and what must be is the bread-and-butter of philosophy. In philosophy of mind, for example, it is contended that some of the best arguments for dualism hinge on a modal premise. In recent years there has been a resurgence of debate about the merits of modal arguments for dualism, and this has in turn sparked interest in modal arguments generally. What makes for a good modal argument? How do we know that the crucial modal premises of such arguments are true? Hume offers the traditional answer in the Treatise: “ ‘Tis an established maxim in metaphysics, That whatever the mind clearly conceives includes the idea of possible existence, or, in other words, that nothing we imagine is absolutely impossible” (I.ii.2, emphasis removed). Hume is certainly right about this much: many in philosophy presume this established maxim. We take ourselves to have some knowledge of what could be, or what could have been, and by this we mean knowledge of metaphysical possibility. Hume does not tell us, however, how this “established maxim” has been established. The more we consider the maxim, the more it cries out for explanation. What is it to conceive something? Why is it that conceiving, so understood, provides evidence for possibility? I think it is fair to say that we lack clear and satisfying positive answers to these questions; what we have instead is a general unease about the central philosophical practice of making claims about the possible and a particular dissatisfaction with “controversial” modal premises in arguments whose conclusions we don’t like. Part of the problem is that many candidate answers to the “what” question quite obviously lead nowhere. ‘Conceive’ is a word with many senses, and many of these senses are clearly unsuitable to play the role of evidence for possibility. Merely understanding, thinking, or entertaining a proposition is not sufficient, for it is easy enough to understand, think, or entertain thoughts about what is necessarily false. The same goes for assuming, supposing, and taking for granted. If the kind of conceiving that philosophers have in mind isn’t any of these, it is less obvious what the right kind is. (“Clear and distinct conception” anyone?)