Kripke and Dualism - Making Up Minds

I wanted to write a bit about Saul Kripke because I figured there are many people who have encountered him through linguistics and logic, but are unfamiliar with how his work has impacted discussions of mind-body dualism.

In this post, I’ll present an argument for dualism. I’m not actually a dualist, but I think it’s an interesting argument. I’m going to focus on the part of the argument involving what are called rigid designators.

I’ll gloss over the first part of the argument for now, and come back to it briefly at the end. For reasons that will become clearer, I’m going to assign a name to my body: let’s say “Benny.” Now here’s the first part of the argument:

Premise 1. I can conceive that the proposition $I \neq Benny$ is true.
Premise 2. If I can conceive a proposition to be true, then the proposition is possible.
Conclusion 1: The proposition $I \neq Benny$ is possible.

So this is a conceivability argument, and as mentioned recently, conceivability arguments are really about what is rationally coherent. Conclusion 1 is about metaphysical possibility, not nomological possibility. In other words, it could be true in some possible world — not necessarily this world. It is clearly a valid argument — we’ll come back later to the question of whether it is sound.

Now we get to rigid designators. If a term T1 picks out the same thing in every possible world, we say that it is a rigid designator. For example, “Gabriel Murray” would pick me out in every possible world.

(At this point, you might want to object that there is a possible world where I have a different name, say “Gordon Murphy.” But the term “Gabriel Murray” in our world still picks out me in that other possible world where I am named Gordon.)

In contrast, “CEO of Twitter” is not a rigid designator, because there is a possible world where Jack is not the CEO, and Dril is CEO instead. In other words, “CEO of Twitter” can pick out different things in different possible worlds.

Now here is how Kripke ties together rigid designators and the idea of necessity: if terms T1 and T2 are both rigid designators, and the identity statement $T1 = T2$ is true, then it is necessarily true. That is, it’s true in every possible world.

Okay, let’s use that to continue our argument for dualism, noting the key fact that “I” and “Benny” are both rigid designators.

Premise 3: If $I = Benny$ is true, it is necessarily true.

But remember Conclusion 1 from above: The proposition $I \neq Benny$ is possible. So from Conclusion 1 and Premise 3 we get the following:

Conclusion 2: $I \neq Benny$

To recap: we said that if $I = Benny$ is true, it has to be true in every possible world, but Conclusion 1 said that it’s possible that $I \neq Benny$ is true in some world. So it cannot be the case that $I = Benny$ .

I’ll make a couple of brief comments about this argument, and then perhaps come back to it in a follow-up post:

Conclusion 2 just says that I am not identical to my body. This is not necessarily a rejection of materialism. It could be that I am identical to [my body + something else material], for example. Many people who describe themselves as dualists want something stronger: namely, to have an immaterial self or spirit of some kind. This argument doesn’t give that conclusion.
I think most philosophers in this area agree with Kripke’s Premise 3, so if they want to challenge the argument, they are more likely to challenge Premises 1 or 2. For example, you could say that $I \neq Benny$ isn’t actually conceivable, or begs the question.

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