So far we have discussed three views of the nature of the mind and mental properties: dualism, behaviorism, and identity theory. We have seen that each faces serious problems. The last view of the nature of the mind and mental properties we will discuss — functionalism — was in large part constructed to solve these problems.
In “Psychophysical and theoretical identifications”, Lewis introduces functionalism via his example of the detective story:
“We are assembled in the drawing room of the country house; the detective reconstructs the crime. That is, he proposes a theory designed to be the best explanation of phenomena we have observed: the death of Mr. Body, the blood on the wallpaper, the silence of the dog in the night, the clock seventeen minutes fast, and so on. He launches into his story:
X, Y and Z conspired to murder Mr. Body. Seventeen years ago, in the gold fields of Uganda, X was Body’s partner... Last week, Y and Z conferred in a bar in Reading... Tuesday night at l1:17, Y went to the attic and set a time bomb... Seventeen minutes later, X met Z in the billiard room and gave him the lead pipe... Just when the bomb went off in the attic, X fired three shots into the study through the French windows...
And so it goes: a long story. Let us pretend that it is a single long con- junctive sentence.
The story contains the three names ’X’, ’Y’ and ’Z’. The detective uses these new terms without explanation, as though we knew what they meant. But we do not. We never used them before, at least not in the senses they bear in the present context. All we know about their meanings is what we gradually gather from the story itself.” (250)
The point of this is that there is a sense in which the story describes, or purports to describe, three people. ‘X’ stands for whoever did the stuff the story ascribes to ‘X’, ‘Y ’ stands for whoever did the stuff the story ascribes to ‘Y ’ etc. Another way to put that is that there is a certain role in the story corresponding to each of these letters. For the letter to stand for a person is for the person to realize that role:
“Suppose that after we have heard the detective’s story, we learn that it is true of a certain three people: Plum, Peacock and Mustard. If we put the name ’Plum’ in place of ’X’, ’Peacock’ in place of ’Y’, and ’Mustard’ in place of ’Z’ throughout, we get a true story about the doings of those three people. We will say that Plum, Peacock and Mustard together realize (or are a realization of) the detective’s theory.” (251)
Lewis’s idea is that words for mental states, like ‘feels pain’ and ‘believes that there is beer in the fridge’, are like the letters in the detective story: they stand for whatever state realizes a certain role.
In the case of mental properties, in place of a detective story we have a story about the connections between various kinds of mental states. For example, our story might include claims like the following:
If someone is placed in front of an open refrigerator which has beer in it, then he will believe that there is beer in the refrigerator.
If someone wants beer and believes that there is beer in the refrigerator, then he will go to the refrigerator and get a beer.
If someone believes that there is beer in the refrigerator, then he believes that there is beer somewhere.
If someone believes that there is a Budweiser in the refrigerator, then he believes that there is beer in the refrigerator.
If someone intends to get a beer out of the refrigerator, then he believes that there is a beer in the refrigerator.
If we think of claims like these as comprising a (somewhat boring) story, then the story has a number of ‘characters’. One of these characters is the belief that there is beer in the refrigerator:
If someone is placed in front of an open refrigerator which has beer in it, then he will believe that there is beer in the refrigerator.
If someone wants beer and believes that there is beer in the refrigerator, then he will go to the refrigerator and get a beer.
If someone believes that there is beer in the refrigerator, then he believes that there is beer somewhere.
If someone believes that there is a Budweiser in the refrigerator, then he believes that there is beer in the refrigerator.
If someone intends to get a beer out of the refrigerator, then he
believes that there is a beer in the refrigerator.
As in the detective story, let’s introduce a label for the belief that there is beer in the refrigerator; let’s call it ‘state X’:
If someone is placed in front of an open refrigerator which has beer in it, then he will be in state X.
If someone wants beer and is in state X, then he will go to the refrigerator and get a beer.
If someone is in state X, then he believes that there is beer somewhere.
If someone believes that there is a Budweiser in the refrigerator, then he is in state X.
If someone intends to get a beer out of the refrigerator, then he is in state X.
As in the case of the detective story, corresponding to this label ‘state X’ is a certain role in the story: ‘state X’ stands for whatever state one is in when one is in front of an open refrigerator which has beer in it, and which, together with the desire for beer, causes one to go to the refrigerator and get a beer, and which one is in when one believes that there is a Budweiser in the fridge ....
In the case of the detective story, we said that a person could realize one of the roles in the story if they did all of the things which the role included. Just so, in this case, we can say that an internal state of a person can realize the ‘state X’ role in our story if it does all of the things included in the role.
If you understand all of that, then you can understand functionalism. Functionalism is the idea that we can tell a (much longer) story like this for every mental property. Each one of these stories defines, corresponding to each mental property, a certain role (sometimes called a functional role). What it is for someone to have that mental property, according to the functionalist, is for them to have some state which realizes that role.
How does functionalism aim to solve the problems we have seen for the other three views of mental properties we have discussed?