Lewis vs. Orthodox FunctionalismLewis's view of the mind superficially looks a lot like functionalism, but in fact, it's really a sophisticated version of Identity Theory.
To understand the difference between Lewis's view and the views of orthodox functionalists, we have to distinguish between role states and realizer states.
Role States vs. Realizer StatesWhat do all these things have in common: a red apple, a round table, a rich man, and a ritzy nightclub? They all have the property of having some property whose name in English starts with the letter "r." That is a second-order property. It's a second-order property because it's a property of having some (ordinary, first-order) property or other which meets some condition.
Whenever we talk about the causal roles played by a device's states, we can distinguish between two sorts of states the device is in. There is:
An example may help to make this distinction clear. Recall the notion of a disposition, from our discussion of behaviorism. We can talk about role states and realizer states with dispositions. With the disposition of fragility, there is the state of having some underlying state or other which will cause the item to break when struck. This is the role state for fragility. All fragile objects share this role state. In different fragile objects, though, this role state is realized by different underlying facts. In a wine glass, the fragility is realized by a certain kind of crystal structure. In a soap bubble, it is realized by certain kinds of tension in the object. So the glass and the soap bubble are in different realizer states, but the same role state.
The functionalist says that mental states like pain are each associated with a certain causal role. In this case, too, we can distinguish between:
Functionalism vs. Identity TheoryIn a nutshell, the functionalist identifies mental states with role states, whereas the Identity Theorist identifies mental states with realizer states.
So, for example, if what realizes the pain-role in humans is firing C-fibers, then the Identity Theorist will say that being in pain is just having firing C-fibers. Creatures without C-fibers can not be in that state. The functionalist, on the other hand, says that pain is the state of having the pain-role played by some internal state or other. (Having firing C-fibers is but one way to do this. Creatures without C-fibers can also be in this role state.)
As I said, Lewis holds a sophisticated version of Identity Theory. He also employs the Ramsey/Lewis method of defining theoretical terms, though, so you might initially miss the difference between his view and the functionalist's view.
The difference between Lewis's use of the Ramsey/Lewis method and the functionalist's use of this method is the following. Let our theory be T[...pain...other mental states...].
the state pain = the state which plays the role specified in Tthat is,
the state pain = the state x1 such that x2...xn T[x1 x2...xn]Here, pain is the occupant of the causal role specified in T. Lewis identifies pain with the realizer state for pain. (This is also the view favored by Braddon-Mitchell and Jackson, in Ch. 6 of their book.)
The orthodox functionalist (e.g., as characterized by Block), says:
the state pain = the state of being a person A who has the role specified in T playedthat is,
the state pain = the state of being a person A such that x1 x2...xn T[x1 x2...xn] and A has x1Here, pain is the state of having the causal role occupied, by some internal state or other. The functionalist identifies pain with the role state for pain.
Martian PainAlthough Lewis identifies pain with the realizer state for pain, he wants to allow that creatures who are biologically quite different from us can nonetheless be in pain. So what he suggests is the following. There is a single causal role associated with pain. For a given species or population S, we take the state which realizes that causal role for typical members of the species. This state will be pain-for-that-species. For instance, having firing C-fibers will be pain-for-humans. Other species will realize the causal role in different ways. So, on Lewis's view, pain-for-those-other-species will be a different sort of state.
Note the difference between Lewis's view and the orthodox functionalist's view. The orthodox functionalist says that pain in humans is the very same state as pain in other species. It's just that pain might be realized differently in the different species. Lewis, on the other hand, denies that pain is the same state in different species. He grants that each species' state of pain plays the same causal role. But, on his view, pain in the one species is a different state than pain in the other species.
Lewis's Argument for Identity TheoryLewis's argument for Identity Theory is different than Smart's argument. Recall that Smart appealed to scientific evidence and also to considerations of simplicity, to show that sensations are identical to brain processes. Lewis gives a different argument for Identity Theory, one which does not appeal to considerations of simplicity.
Lewis's argument goes as follows:
This argument is valid, and we can suppose that our neurophysiological evidence supports some claim like premise 2. So everything turns on premise 1.
Lewis claims that premise 1 is implicit in our understanding of the concept PAIN, and hence that we can know premise 1 to be true a priori. However, this claim is very contentious. Note that premise 1 identifies pain with the realizer state for causal role R. So only someone who holds an Identity Theory like Lewis's will grant that premise 1 is true and knowable a priori.
Some functionalists (common-sense functionalists) agree with Lewis that there is some a priori connection between our concept of pain and causal role R. However, in their view, what we can know a priori about pain is not premise 1, but rather:
1*. Pain = what is had in common by all the people who have some state or other occupying causal role R.This premise identifies pain with the role state for causal role R. If we replace premise 1 in Lewis's argument with premise 1*, then the argument is no longer valid. So Lewis has to tell us why the a priori connection between our concept of pain and causal role R takes the form specified in premise 1, rather than the form specified in premise 1*. He has to explain why we should believe that it's premise 1 which is true and knowable a priori, rather than premise 1*.
The reason why Lewis prefers to identify pain with a realizer state, rather than a role state, is that, in Lewis's view, only realizer states have any causal efficacy. He thinks role states are unable to do any causal work. An analogy: when you strike a glass and it breaks, does the glass's fragility play any role in causing the glass to break? Or is all the causal work done at the microphysical level? In Lewis's view, only the microphysical states that realize the glass's fragility do any causal work. The role state of fragility is causally inert. Similarly, Lewis believes that when a person is in pain, the role state associated with the pain is also causally inert. All the causal work is done by the person's being in the neurophysiological states that realize the pain role.
When you burn your hand on a hot stove, it does seem intuitively correct to say that the pain in your hand causes you to pull your hand back. Indeed, the functionalist trumpeted it as one of the advances of his view over behaviorism that, on his view, mental states are real inner causes of our behavior. So if a theory of the mind says that certain mental states are causally inefficacious, that is a mark against that theory. If Lewis's views about mental causation are correct, then identifying pain with the neurophysiological states that realize the pain role is the only way to make pain be causally efficacious. This would be a big advantage for Lewis's Identity Theory.
Lewis's views about mental causation are very controversial, however. Other philosophers argue that both the neurophysiological states that realize pain and the role state for pain are causally efficacious. They just produce the same effect. We will return to this debate later in the course.