In the last two posts (here and here) we discussed dualism, the view that a person, the subject of mental states, is something more than his or her physical body. We’ve examined a type of empirical argument for dualism. Empirical arguments are arguments based on sense experience. The type of empirical argument that we’ve examined is one that tries to show that there exists a feature F that people possess, a feature that we know about through sense experience, but a feature which couldn’t be possessed by something entirely physical, such as body or a brain. According to some philosophers, we don’t understand how consciousness is located in something physical. But, given that the dualist has the burden of proof, he needs to show more than the fact that we lack this understanding. He has to show that consciousness couldn’t be supported or housed in something entirely physical. The most promising candidate for such a feature F are near-death experiences. However, we concluded that such an appeal might give us some reason to believe in dualism, but it’s not a conclusive reason. If we cannot give any reasons to believe that dualism is true, we should be tentative at best in accepting the view, given that it has the burden of proof. But empirical arguments are not the only way philosophers have tried to establish dualism. Some philosophers have tried to argue for dualism in a non-empirical way – not based on what we can sense – but rather on what we can imagine or conceive. I call these types of arguments “philosophical” arguments for dualism.
Here is one of the most famous philosophical arguments for dualism. It is very similar to an argument given by the famous French philosopher Rene Descartes in the 17th century.
- You can coherently imagine yourself without your physical body.
- If you can coherently imagine X, then you have reason to believe that X is metaphysically possible.
- So you have reason to believe that it is metaphysically possible for you to exist without your physical body.
- If it is metaphysically possible for you to exist without your physical body, then you are not the same as your physical body.
- Therefore, you have reason to believe that you are not the same as your physical body. [Dualism is true!]
Let’s begin to think about this argument by examining premise 1. You can imagine many things. You can imagine yourself being President of the United States. You can imagine yourself flying. You can imagine that you were born on the moon. You can imagine yourself traveling back in time. But you cannot imagine everything. Can you imagine yourself existing and not existing at the same time? I can’t imagine this. What is relevant for our argument is whether you can imagine yourself without your physical body. Many people think they can. Perhaps you can imagine having a near-death experience, “floating” outside of your body and seeing your body. You might not be able to imagine seeing without eyes or a brain. If you can’t imagine being disembodied, then try imagining yourself existing in a different physical body. For example, imagine all the parts of your body, including your internal organs, being gradually replaced by artificially made parts. In this scenario, imagine that the neurons of your brain are gradually replaced with electronic circuits that function in the same way as your neurons. If you can imagine surviving the piecemeal replacement of your entire physical body, including your brain, then you can imagine yourself in a different physical body, an artificial one. And this means that you have reason to believe premise 1. Does it mean that premise 1 is true? No. It may be that you’re not coherently imagining what you think you’re imagining. We will discuss this idea of coherent imagining below.
Let’s turn to premise 2. In order to understand this premise, as well as the the rest of the argument, you need to understand what it means to say that something is “metaphysically possible“. To explain this I will use a diagram from this lecture given by the philosopher Jim Pryor.
Pryor points out the term “possible” has different meanings.
If someone comes up to you on the street and says “It’s possible that I was born on the moon,” you’ll most naturally take him to be making some sort of (crazy) claim about what it’s reasonable for him to believe really is the case. You’d be understanding his claim as “For all I know, I was born on the moon.” This is a use of “possible” to express claims about evidence and knowledge. It’s called an epistemic sense of possibility.
But there is another thing the guy might have meant. He might have meant, “Look, I know I was born on the Planet Earth. But things could have gone differently. I could have been born on the moon–if for instance mankind had colonized the moon in the 1800s.” Here he’s using “possible” not in the sense of “for all I know…” but rather in a metaphysical sense. He’s not talking about what he knows. He’s talking about what could have happened, if the world or history had been different in certain ways. We call claims of this latter sort claims about metaphysical possibility.
Here’s a rule of thumb to help you out. If something of this sort is ever true:
If the world were to be different in such-and-such ways, then P would be the case
then P is metaphysically possible. If nothing of that sort is true, then P is metaphysically impossible. There’s no way the world could be such that P would be the case. If something is compatible with our laws of physics–if the laws of physics would permit it to happen–then we say that that thing is both metaphysically possible and physically possible.
Many philosophers think things can be possible in a metaphysical sense, even if they’re contrary to our actual laws of physics, and so physically impossible. For example, the charge of an electron might have been larger; or the gravitational constants might have been slightly different. We know that, as things stand, the world is not that way. And if the world had been that way, then perhaps life as we know it would not have come about. But it still seems possible, in a broad sense, for the world to have been that way. Physicists sometimes talk about, and advance hypotheses about, what the world would be like if the laws of physics or the fundamental physical constants had been slightly different.
It’s important to be clear about what this bottom category, “metaphysically impossible,” means. What it means is that that is not a way the world could have been. Let’s try to come up with some things that would be examples of this. Would it have been possible for the world to contain 3-sided squares? What would such a world be like? That doesn’t really seem to be a possible way for the world to be, does it? Nor does it seem to be possible for it to be raining and not raining in the same place at the same time. Nor does it seem to be possible for a person to exist and fail to be one and the same person as himself. There are no possible situations in which things of those sort take place. They all seem to be metaphysically impossible.
According to Pryor there are at least three senses of “possible”, an epistemic sense, a physical sense and a metaphysical sense. For our purposes, you can ignore the epistemic sense and focus on the physical and metaphysical sense. Everything that is actually the case is both physically possible and metaphysically possible. For example, it’s actually the case that there are cars in the United States that are convertibles. This is both physically possible and metaphysically possible. Some things that are physically possible are not actually the case. For example, it’s not actually the case that all the cars in the United States are electric. But this is certainly physically possible. Here is another example. It’s physically possible that Donald Trump was a bachelor when he was elected President. But this was not actually the case. Since it’s physically possible that all cars in the United States are electric and that Donald Trump was a bachelor when he was elected President, both these are also metaphysically possible.
There are things that are physically impossible that are metaphysically possible. For example, it’s physically impossible to travel faster than the speed of light. This is because traveling faster than the speed of light violates the laws of physics. But some philosophers believe that traveling faster than the speed of light is metaphysically possible, since these philosophers believe the laws of physics could have been different, wherein traveling faster than the speed of light would not violate any of these different physical laws. If these philosophers are correct, then traveling faster than the speed of light is not physically possible (since this violates the physical laws that we actually have), but is metaphysically possible (since they are consistent with the physical laws that could have existed).
If traveling faster than the speed of light is metaphysically possible, then is anything metaphysically impossible? Yes. It’s metaphysically impossible for a square to be a circle, for a rose to be not a rose, for there to be two of me, for water not to be identical to H2O, for me to be someone else. These are just some of the examples of things that are metaphysically impossible. There are an infinite number of things that are metaphysically impossible. If something is contradictory with the laws of logic, then it’s metaphysically impossible.
Now that we are beginning to understand the idea of metaphysical possibility, let’s turn to premise 2. Is it true that if you can coherently imagine X, then you have good reason to believe that X is metaphysically possible? Why do philosophers believe it’s metaphysically possible to have been born on the moon or travel faster than the speed of light? It’s because they think they can imagine these situations. Of course, just because you can imagine something doesn’t mean that it is metaphysically possible. For example, I am able to imagine traveling back in time. But this is not metaphysically possible. Here’s why. Suppose I were to travel back in time to a town that has only a 100 people living in it. After I arrive, the town will have 101 people living in it. A town cannot have both 100 people living in it and 101 living in it at the same time. Does this mean that premise 2 is false? No. The premise doesn’t say that imagination guarantees what is metaphysically possible. It just says that coherently imagining something gives us good reason to believe what is metaphysically possible. In the case, of my imagining traveling back, I’m not imagining coherently.
What about the claim that some people make that they can imagine being disembodied? Are these people imagining coherently? Perhaps not. Perhaps once we learn more about mental states we will see that there is some sort of contradiction in the idea that I can have mental states without about a brain. Even if one cannot coherently imagine being disembodied because it’s metaphysically impossible to be disembodied, it doesn’t follow that it’s metaphysically impossible for a person to exist in a different physical body. I know that it’s physically possible for me to exist with different body parts. I can, for example, continue to exist with artificial arms and legs and heart and lungs. So I have some reason to believe that I can coherently survive the piecemeal replacement of all my body parts, including the neurons in my brain with artificial neurons. Therefore I have reason to believe that it’s metaphysically possible for me to exist with an entirely new body.
So let’s review. It seems that I can coherently imagine existing without my body, maybe not as a disembodied soul, but perhaps in a new artificial body. This gives me reason to believe that my existing in a new body is metaphysically possible. Now, you might think, “So what? Why should the fact that it’s metaphysically possible for me to exist in a new body mean that dualism is true? After all, there are many things that are metaphysically possible that are neither physically possible nor actually the case. It may be metaphysically possible that I can travel faster that light. But, as we pointed out above, this is neither physically possible nor actually the case. So why should it actually be the case that I am more than my body just because it’s metaphysically possible that I am more than my body?” To answer this we need to turn to premise 4.
Premise 4 states that if it is metaphysically possible for me to exist without my physical body, then I am not the same as my physical body. The idea behind this premise is that if I am identical with my body, then I and my body are just one and the same thing. But if I and my body are just one thing, then how would it be metaphysically possible for me and my body to come apart and be two things? It seems that my body and I cannot come apart if we are just one thing. So if it’s metaphysically possible for me and my body to come apart, then I am not actually the same as my body. In short, I and my body are in actual fact two separate things. This means dualism is true.
