Even if the dualist managed to find some property that your mind plausibly does have and physical objects like your brain plausibly lack, and appeal to that property didn’t seem to essentially involve people’s perspective on things in the problematic ways we were just looking at, how much would that accomplish?
At best it would only show that the mind isn’t identical to the physical objects in question. As we saw last week, though, the materialist always has the option of denying that the mind is any kind of substance or object. They could say that minds are more like hikes or dances. What makes them a materialist is that they think all the objects there are, are physical. But they don’t have to say that the minds are some of those physical objects, anymore than we have to say that hikes or dances are.
Summing up, in response to the kinds of Leibniz’s-Law-based arguments for dualism we’ve seen so far, a materialist/physicalist would make one (or more) of these objections:
the dualist may be equivocating, instead of using notions in a single consistent way for her whole argument
the dualist may be begging the question, that is, relying on a premise that’s too controversial/disputed to help settle a debate about whether to accept dualism
the dualist may be applying Leibniz’s Law illegitimately in ways that exploit different perspectives, as in the arguments we attributed to Lex Luthor
these Leibniz’s-Law-based arguments can at best show that minds aren’t identical to a physical object/substance. But that’s not yet “the right shape” of argument to establish dualism. One could agree with that conclusion, without yet accepting that minds are identical to a different kind (a non-physical, esssentially thinking) object/substance, as the dualist wants. One could still be a materialist/physicalist, while denying that minds are any kind of object/substance.
Here’s a different kind of strategy the dualist might appeal to, in support of their view. Like some of the arguments we considered before, it starts with the premises that:
But now, the dualist doesn’t appeal to Leibniz’s Law. Instead, they appeal to the fact that there’s a kind of possibility — sometimes called “logical possibility” or “metaphysical possibility” — where the fact that we can imagine something is how we primarily tell that things are possible in that sense. So if we can imagine our minds existing without any bodies, then it seems to be in some sense possible for our minds to exist without any bodies. And then the dualist will try to argue, for this to even be possible, it has to be the case that right now, in actuality, our minds are separate from any physical substances.
Descartes seems to be working with an argument of this sort in his Second and Sixth Meditations.
In order to get a better handle on this reasoning, we’ll have to spend some time digging into this notion of possibility, and what connections it has to what we can and can’t imagine. We’ll take these issues up in a few classes.
First, though, we’ll turn to some arguments on the other side, that materialists/physicalists appeal to against dualism.