E-044 SEP FUNC - Functionalism (Thesis 1 Excerpt)

Exact excerpt

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## 1. What is Functionalism?
Functionalism is the doctrine that what makes something a thought, desire, pain (or any other type of mental state) depends not on its internal constitution, but solely on its function, or the role it plays, in the cognitive system of which it is a part. More precisely, functionalist theories take the identity of a mental state to be determined by its causal relations to sensory stimulations, other mental states, and behavior.
For (an avowedly simplistic) example, a functionalist theory might characterize _pain_ as the state that tends to be caused by bodily injury, to produce the belief that something is wrong with the body and the desire to be out of that state, to produce anxiety, and, in the absence of any stronger, conflicting desires, to cause wincing or moaning. According to this theory, all and only creatures with internal states that can meet this condition, or play this role, are capable of being in pain, and an individual is in pain at time _t_ if and only if they are in a state that is playing this role at _t_.
Suppose that, in humans, there is some distinctive kind of neural activity (C-fiber stimulation, for example) that plays this role. If so, then according to this functionalist theory, humans can be in pain simply by undergoing C-fiber stimulation. But the theory permits creatures with very different physical constitutions to have mental states as well: if there are silicon-based states of hypothetical Martians or inorganic states of hypothetical androids that also meet these conditions, then these creatures, too, can be in pain. As functionalists often put it, pain can be _realized_ by different types of physical states in different kinds of creatures, or _multiply realized_. (See entry on [multiple realizability](https://plato.stanford.edu/entries/multiple-realizability/).) Indeed, since descriptions that make explicit reference only to a state’s causal relations with stimulations, behavior, and one another are what have come to be known as “topic-neutral” (Smart 1959) – that is, as imposing no logical restrictions on the nature of the items that satisfy the descriptions – then it’s also logically possible for _non_ -physical states to play the relevant roles, and thus realize mental states, in some systems as well. So functionalism is compatible with the sort of dualism that takes mental states to cause, and be caused by, physical states.
Still, though functionalism is officially neutral between materialism and dualism, it has been particularly attractive to materialists, since many materialists believe (or argue; see Lewis, 1966) that it is overwhelmingly likely that any states capable of playing the roles in question will be physical states. If so, then functionalism can stand as a materialistic alternative to the Psycho-Physical Identity Thesis (introduced in Place 1956, Feigl 1958, and Smart 1959, and defended more recently in Hill 1991, and Polger 2011), which holds that each type of mental state is identical with a particular type of _neural_ state. This thesis seems to entail that no creatures with brains unlike ours can share our sensations, beliefs, and desires, no matter how similar their behavior and internal organization may be to our own, and thus functionalism, with its claim that mental states can be multiply realized, has been regarded as providing a more inclusive, less “(species-) chauvinistic” (Block 1980b) – theory of the mind that is compatible with materialism. (More recently, however, some philosophers have contended that the identity thesis may be more inclusive than functionalists assume; see Section 6 for further discussion.)
Within this broad characterization of functionalism, however, a number of distinctions can be made. One of particular importance is the distinction between theories in which the functional characterizations of mental states purport to provide analyses of the meanings of our mental state terms (or otherwise restrict themselves to a priori information), and theories that permit functional characterizations of mental states to appeal to information deriving from scientific experimentation (or speculation). (See Shoemaker 1984c, and Rey 1997, for further discussion and more fine-grained distinctions.) There are other important differences among functionalist theories as well. These (sometimes orthogonal) differences, and the motivations for them, can best be appreciated by examining the origins of functionalism and tracing its evolution in response both to explicit criticisms of the thesis and changing views about the nature of psychological explanation.
## 2. Antecedents of Functionalism
Although functionalism attained its greatest prominence as a theory of mental states in the last third of the 20th century, it has antecedents in both modern and ancient philosophy, as well as in early theories of computation and artificial intelligence.
### 2.1 Early Antecedents
The earliest view in the Western canon that can be considered an ancestor of functionalism is Aristotle’s theory of the soul (350 BCE). In contrast to Plato’s claim that the soul can exist apart from the body, Aristotle argued (_De Anima_ Bk. II, Ch. 1) that the (human) soul is the _form_ of a natural, organized human body – the set of powers or capacities that enable it to express its “essential whatness”, which for Aristotle is a matter of fulfilling the function or purpose that defines it as the kind of thing it is. Just as the form of an axe is whatever enables it to cut, and the form of an eye is whatever enables it to see, the (human) soul is to be identified with whichever powers and capacities enable a natural, organized human body to fulfill its defining function, which, according to Aristotle, is to survive and flourish as a living, acting, perceiving, and reasoning being. So, Aristotle argues, the soul is inseparable from the body, and comprises whichever capacities are required for a body to live, perceive, reason, and act. (See Shields, 1990, and Nelson, 1990, for further debate about whether Aristotle’s view can be considered to be a version of functionalism.)
A second, relatively early, ancestor of contemporary functionalism is Hobbes’s (1651) account of reasoning as a kind of computation that proceeds by mechanistic principles comparable to the rules of arithmetic. Reasoning, he argues, is “nothing but _reckoning_ , that is adding and subtracting, of the consequences of general names agreed upon for the _marking_ and _signifying_ of our thoughts.” (_Leviathan_ , Ch. 5) In addition, Hobbes suggests that reasoning – along with imagining, sensing, and deliberating about action, all of which proceed according to mechanistic principles – can be performed by systems of various physical types. As he puts it in his Introduction to _Leviathan_ , where he likens a commonwealth to an individual human, “why may we not say that all automata (engines that move themselves by springs and wheels…) have an artificial life? For what is the heart but a spring; and the nerves but so many strings, and the joints but so many wheels…”. It was not until the middle of the 20th century, however, that it became common to speculate that thinking may be nothing more than rule-governed computation that can be carried out by creatures of various physical types.
### 2.2 Thinking Machines and the “Turing Test”