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>> . So substantialism posited two types of
stuff, immaterial stuff and physical stuff.
And the problem with causation says, well how can this immaterial stuff interact
with the physical stuff? As I said, there are other problems with
substantialism, 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. But, 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, are logical behaviorism, identity theory
and functionalism. We won't be looking at logical behaviorism
today. But I'll put some references on the hand
out so that you can look it up if you're interested.
The first view 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 a thought, my thought that I'm 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 are
going on in me at the time. But 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
realisation 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 in 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 two things are
physically indiscernible, then they're going to be psychologically indiscernible.
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 re-described in purely physical terms.
It can be re-described in terms of a mix of chemistry and hormones and atomic
structures, that are going on in that, in my body, right now.
Now there are different ways to spelling out the identity of relation between our
psychological thoughts and physical structures that realize them, that make
them up. This is quite a tricky area of philosophy,
and I put some work on the handout to talk you through some of the relations they
might, that there might be. But here are the two that are important.
If your 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 where 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.
So I 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 Crufts, then I'd be asking about types.
I'd be asking I'd be being asked about how many types of dogs there were at Crufts.
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 in at the time. Type identity is making a stronger claim.
Type identity is saying that particular types of physcological states, say pains,
are identitical with particular types of physical states.
Say, for example, the neural realization of pains might be, as philosophers often
refer to, C fibers firing. I realize that this probably isn't the
neural realization of pain, but that's what is said in philosophy textbooks.
So, when we're talking about type identity, we're saying that a type of
psychological state, pains, are identical with types of physical states that 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 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 realizers.
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 a 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.
There'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. But if you'd like to carry on and come
back to it later, then that will be okay as well.
On the face of it, identity theory seems to be very persuasive.
It sticks with stuff that we know about in 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 in 1967, pointed out some problems with identity theory.
The main problem is that he thought that it was too 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 of
slightly different chemicals to human brains.
And yet we don't want to say that octopuses 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? Well, identity theory is saying that each
type of 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 that octupuses can feel pain.
But octopi don't have the same sort 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, 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 their pain identical with? We want to say that their pain is
identical with a 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 states 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, or
within the species, or do we want to make a more universal claim?
Now the kind of thing that Putnam pointed out with this 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 those brain structures vary so
dramatically across species. It seems to be the case that humans with
their physical makeup, and octopi with their physical makeup, and intelligent
aliens with their physical makeup can all feel pain.
They can all have a sensation of pain, even though the stuff that they're made of
is very different. So what allows us to say that these three
types of things are in pain, humans, octopi and aliens?
Putnam says that this points to a more fundamental feature of psychological
states. When you'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 known as the issue of multiple
realisability. What Putnam was saying is that a
particular psychological state, like pain, can have different physical realisers, can
be made of different physical stuff dependent on whether you're 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 phsycial state
that realizes the psychological state of pain can be very different, depending on
the type of organism that we're looking at.