(Note: The past couple weeks, the Friday Questions have come from students in the first-year QUB Human Nature module. There are a couple more questions queued up for posting from these students, but I will save them for next week.)
For this Friday Question, I want to address a question in modal epistemology.
In philosophy, we are very often interested in what could have been or what has to be rather than what merely happens to be the case. For instance, philosophers interested in the mind-body problem are interested in knowing not just whether there are correlations between instances of mentality and certain patterns in the distribution of physical properties, but whether these correlations are indicative of some sort of metaphysically necessary connection between mind and body rather than a correlation that happens to be due to, say, natural laws that could have been otherwise. Knowing whether there is a metaphysically necessary connection or not seems crucial to addressing whether mind is distinct from body in the way that Descartes suggested.
One might reasonably wonder about the source of our grasp on what is metaphysically necessary or metaphysically possible (assuming, of course, that we have any such grasp). Modal epistemology is the study of what this grasp consists in.
One particular prominent school in modal epistemology is modal rationalism. According to modal rationalism, knowledge of the metaphysical necessity or possibility is always attained via purely rational abilities. For instance, it might be grounded in knowledge of what sorts of scenarios are "conceivable," where the conceivability of a scenario is something that we can test out by deploying our rational abilities. A better word for conceivability might be "intelligibility." The idea is that we can rule out the metaphysical possibility of a scenario by appreciating that the scenario doesn't make any sense or fails to be coherent; at the same time, we can confirm the metaphysical possibility of a scenario by appreciating that it does make sense or is coherent.
Certain examples (made prominent by Saul Kripke) force us to revise this last thought. For instance, from a position of ignorance it appears it would be coherent for Kim to think that Jack O'Hearts, a cheesy secret admirer, is distinct from her best friend John even if, actually, John just is Jack O'Hearts. Presumably, it isn't metaphysically possible for one and the same person not to be himself, so it isn't metaphysically possible for Jack O'Hearts to be anybody but John, or vice-versa.
The modal rationalist can respond to this situation by suggesting that although intelligibility isn't sufficient for metaphysical possibility, that is only because the intelligibility of a scenario may presuppose certain things about the actual world that are false. For instance, the intelligibility of the scenario in which Jack O'Hearts is not John may require the presupposition that the actual world is such that Jack O'Hearts is not John. If we were to suppose instead that in actual fact this is one and the same person, the scenario in which this identity doesn't hold no longer makes sense. The suggestion would then be that intelligibility is sufficient for metaphysical possibility so long as the intelligibility does not presuppose anything false about the actual world.
Is this form of modal rationalism viable?
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