Phil 101: Leibniz’s Law, part 4

How Much Could Leibniz’s Law Show, Anyway?

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:

A Different Strategy for the Dualist

Yhere are other, more promising strategies 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.

The philosopher Descartes seems to be employing an argument like this in his Second and Sixth Meditations.

In this course, we’re not going to have the time to explore these arguments, or the different philosophical issues they raise. We’ll just note that there are other strategies for arguing for dualism than the ones we’ve looked at so far, which weren’t that successful.

And look, even if the dualist weren’t able to come up with a really compelling argument for their view, the view might nonetheless still be correct. Sometimes things are true even if nobody can prove—or even if nobody knows—that they are true. So materialists shouldn’t get too pleased with themselves when all they’ve managed to do is criticize some arguments for dualism. If they want to argue for their own view, and so against dualism, they’re going to have to do more work. This is what we’ll take up next.