So, substance dualism posited two types of stuff, immaterial stuff and physical stuff. And the problem of causation says, well, how can this immaterial stuff interact with the physical stuff? As I said, there are other problems with substance dualism. But this is a particularly pressing one. Now perhaps the easiest way to get around this problem is to get rid of the immaterial stuff. Just say there’s only physical stuff in the world. This is the view that is known as physicalism, or materialism. Physicalism is the view that minds and bodies are made of exactly the same thing. So, my thoughts about going on holiday to Paris or my desires to have a nice lunch later on, are made out of exactly the same sorts of stuff as my toenails. Well, not physically the same sort of stuff. It's made out of physical material, which can be found up here in my brain. So this mix of chemicals and hormones and H2O make up my thoughts. Now there are different ways of spelling out the view that is physicalism, and we're going to look at two today. The three different ways that there are logical behaviorism, identity theory, and functionalism. We won't be looking at logical behaviorism today, but I'll put some references on the handout so that you can look it up if you're interested. The first theory I'd like to look at today is identity theory. Now, the clue's in the name here. Identity theory says that thoughts, such as my thought that am going to go to Paris next week, is identical with a particular physical state of my body and brain. So that physical state can accommodate all the different molecular changes that's going on in me at the time. If we could freeze those molecular changes at a particular point, that point at which I'm thinking, I'm going to go to Paris next week. Then what we have there is what's known as the physical realization of my thought that I'm going to go to Paris next week. Now physicalism says that if you have two organisms that are physically identical. So imagine you have two organisms and you can't tell them apart just looking by their physical features. They have exactly the same amount of hormones. They're exactly the same molecular structure, identical all the way down. Then those two organisms will be in exactly the same psychological state. That is a commitment that the physicalist has to make. Because if she's saying that mental states just are physical states, then she has to say that if the two things are physically indiscernable, then they're going to be psychologically indiscernable. Identity theory is also a reductionist view. It's reducing the psychological thoughts that we have to the physical. It's saying that if we think very carefully, the thought that I'm going to go to Paris next week can be redescribed in purely physical terms. It could be redescribed in terms of a mix of chemistry and hormones and atomic structures that are going on in my body right now. Now, there are different ways of spelling out the identity relation between our psychological thoughts and the physical structures that realize them and make them up. It's quite a tricky area of philosophy. And I put some work on the handout to talk you through some of the relations that might be, but here are the two that are important. If you're an identity theorist, if you want to say that psychological states, like thoughts that I'm going to Paris, are identical with particular physical states of the body, then I could be making one of two claims. To understand this let's take a brief detour. Imagine that you said to me, how many dogs were there at Crufts last year? There are two ways I could take that question. I could mean you to say, how many individual dogs were there at Crufts? Some might say, 30,000. Or I might take you to be asking me, how many species of dogs there were at Crufts? In which case I might say, 300. If I was asking about how many individual dogs there were at Crufts, I'm asking about what philosophers call tokens. I'm asking about tokens of dogs, each individual dog. But if the question was about how many species of dogs there were at Croft's, then I'd be asking about types. I'd be being asked about how many types of dogs there were at Cruft's. This is known as a type relation. Okay, let's zoom back to our discussion about the identity theory. How does this fit in? Well, if we're saying that psychological states are identical with physical states, then we're going to have to explain whether we mean token identity or type identity. Token identity would be something like this. We could say that for every psychological state that a human being is in there is a corresponding physical state for it. So for example, you could say that I had a pain in my tummy at 2 o'clock yesterday. Pain is a psychological state. Token identity says that the pain that I had in my tummy yesterday at 2 o'clock was identical to a particular physical state that my body was within at the time. Type identity is making a stronger claim. Type identity is saying that particular types of psychological states, say pains, are identical with particular types of physical states. Say for example the neural realization of pains might b,e as philosophers often refer to, C fibers firing. I realize that this probably isn't the neural realization of pain, but that's what it said in philosophy textbooks. So, when we're talking about type identity, we're saying that a type of psychological state pains our identical with types of physical states the bodies can be in. C fibers being stimulated. So that all human beings, when their C fibers are stimulated, we can say that they're in pain. There's a type of psychological state, and that's an identical with a type of physical state. Now, this is a much stronger claim than token identity, because token identity is just saying, well, for any psychological state there will be a corresponding realizing physical state. Type identity gives us a research program. If you're committed to type identity to types of mental states being identical with types of physical states, then you can try and find out more about say, pains in general by looking at the neural realizes. So just to review, identity theory is a physicalist or materialist thesis. It's saying that there's no immaterial substance in the world. That's crazy talk. All we have is physical stuff. It's reductionist view. It's saying that psychological states, thoughts, feelings, sensations, pains for example, can be reduced to particular physical states in the body. And there are two ways of spelling out the way in which psychological states are identical to physical states in the body. That's token identity and type identity. Now these are quite tricky. So if you need to pause the video and go back to the handout and look through, that's totally fine. If you'd like to carry on and come back to it later then that would be okay as well. On the face of it, identity theory, seems to be very persuasive. It sticks with stuff that we know about the world. It's not positing any extra things like immaterial souls or immaterial minds. It seems to provide us with a good scientific research program. If we look at brains and we look at bodies then we'll find out more about psychological states. However, the philosopher Hilary Putnam, in an iconic paper, 1967, pointed out some problems of identity theory. The main problem is that he thought it was chauvinistic, it's too narrow. Let's think about it in this way. Think about an octopus. Octopuses, octopi, are very different from humans. Their brains are probably made up from slightly different chemicals to human brains. And yet, we don’t want to say that octopus' can't feel pain. That seems a very odd claim to make. Just because your brain isn't like my brain doesn't mean that you can't feel the same things that I feel. Why is this a problem for identity theory? Identity theory is saying that each type is psychological state can be reduced to a particular brain state. So we're saying that pain just is the stimulation of C fibers. But that can't be right because we want to say octopuses can feel pain. But octopi don't have the same sorts of C fibers as human beings. To take an even broader thought experiment, think about if we found a species of alien. Aliens that seemed really intelligent, but their brains are made up of totally different things to us. They’re sort of not even comparable to the human mixture of H2O chemicals and hormones. Maybe they’re made out of wood or something like that. Yet, they seem to be very intelligent. And these aliens also appear to feel pain. They wince when they touch things. They avoid certain things because they say that it gives them an unpleasant sensation. They tell us that they can feel pain. But what is that pain identical with? We want to say that their pain is identical with the brain state, too. A brain state that's totally different from the human brain state. So this seems that we have to qualify the types of identity that we're using. We're saying that pain and other psychological states are identical with particular states of the body, but the state of the body that they're identical with could vary from species to species. And possibly more frighteningly, could even vary across human to human. Well, this greatly reduces the strength of the identity theory. Now this isn't a killer blow for the identity theory. This doesn't completely rule it out altogether. But it does raise a very interesting question about how we should think about the identity relation between psychological states and their physical realizes. Should we think about it as a realization just within a particular human being within the species? Or do we want to make a more universal claim? Now the kind of thing that Putnam pointed out with his paper is that he said look, this clearly seems to be a problem with the identity theory. We clearly need to do a bit more to spell out what the relationship is between the psychological state and the physical state that realizes it. Putnam says, maybe we're looking in the wrong place. Maybe what we shouldn't be thinking about is what psychological states are made of. Maybe it's just wrong to look at brain structures to try and work out what particular psychological states are because these brain structures vary so dramatically across species. It seems to be the case that humans, with their physical make up, and octupi with their physical make up, and intelligent aliens with their physical make up, can all feel pain. They can all have the sensation of pain even though the stuff that they're made of is all very different. So what allows us to say that these three types of things are in pain? Humans, octupi, and aliens? Putnam says that this points to a more fundamental feature of psychological states. When we're thinking about psychological states, we should think about what they do, and not what they're made of. This is the second view that we'll be looking at. And that's known as functionalism. So the problem that Hilary Putnam was pointing out with identity theory is sometimes know as the issue of multiple realisability. What Putnam was saying is that a particular psychological state, like pain, can have different physical realizes, can be made of different physical stuff depending on whether you are a human, whether you're an octopus, or whether you're an alien. We want to say that humans, octopuses and these aliens can still all feel pains, even though the stuff that makes up those pains, the stuff that the identity theorist says the pain is identical with, is completely different. So this is known as multiple realisability. Because the physical state that realizes the psychological state of pain can be very different depending on the type of organism that we're looking at.
