Functionalism and its varieties in Philosophy of Mind

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Functionalism is a philosophical theory that aims to explain mental states and processes in terms of their function or role in a broader system. It is primarily concerned with understanding mental states by focusing on their relationship to the external world rather than their internal makeup or structure. This theory has had a significant impact on various fields, including philosophy of mind, sociology, anthropology, and even computer science.

At its core, functionalism proposes that mental states are not exclusively determined by their physical makeup but rather by the role they play within a larger system. For functionalists, mental states are not dependent on specific materials or physical properties but rather on how they contribute to an individual’s behavior or interaction with the environment. In other words, what matters is what these mental states do or what purposes they serve, rather than their particular physical instantiation.

Functionalism in philosophy of mind attempts to explain mental states such as beliefs, desires, emotions, and perceptions by their functional roles in cognitive systems. It argues that mental states have a causal relationship to behavior and can be identified through their effects both on one’s own thoughts and actions, as well as on those around them. For example, a functionalist would define pain as a mental state that typically causes a person to avoid certain stimuli, enabling them to protect their well-being.

Multiple Realizability

An important part of some arguments for functionalism is the idea of multiple realizability. According to standard functionalist theories, a mental state corresponds to a functional role. It is like a valve; a valve can be made of plastic or metal or other material, as long as it performs the proper function (controlling the flow of a liquid or gas).

Similarly, functionalists argue, a mental state can be explained without considering the state of the underlying physical medium (such as the brain) that realizes it; one need only consider higher-level function or functions. Because a mental state is not limited to a particular medium, it can be realized in multiple ways, including, theoretically, with non-biological systems, such as computers. A silicon-based machine could have the same sort of mental life that a human being has, provided that its structure realized the proper functional roles.

However, there have been some functionalist theories that combine with the identity theory of mind, which deny multiple realizability. Such Functional Specification Theories (FSTs), as they are called, were most notably developed by David Lewis and David Malet Armstrong. According to FSTs, mental states are the particular “realizers” of the functional role, not the functional role itself. The mental state of belief, for example, just is whatever brain or neurological process that realizes the appropriate belief function.

Thus, unlike standard versions of functionalism (often called Functional State Identity Theories), FSTs do not allow for the multiple realizability of mental states, because the fact that mental states are realized by brain states is essential. What often drives this view is the belief that if we were to encounter an alien race with a cognitive system composed of significantly different material from humans’ (e.g., silicon-based) but performed the same functions as human mental states (for example, they tend to yell “Ouch!” when poked with sharp objects), we would say that their type of mental state might be similar to ours but it is not the same. For some, this may be a disadvantage to FSTs. Indeed, one of Hilary Putnam’s arguments for his version of functionalism relied on the intuition that such alien creatures would have the same mental states as humans do, and that the multiple realizability of standard functionalism makes it a better theory of mind.

Varieties of Functionalism

One variety of functionalism is known as machine-state functionalism. It was proposed by Hilary Putnam in the 1960s. This view posits that mental states can be fully understood by analyzing how they fit into a specific causal network within an organism. Proponents of machine-state functionalism argue that a mental state is defined by its causal relations to other mental states, sensory inputs, and behavioral outputs. Simply put, mental states are considered as parts of a larger functional mechanism that interacts with other aspects of an individual’s cognitive system.

In non-technical terms, a Turing machine is not a physical object, but rather an abstract machine built upon a mathematical model. Typically, a Turing Machine has a horizontal tape divided into rectangular cells arranged from left to right. The tape itself is infinite in length, and each cell may contain a symbol. The symbols used for any given “machine” can vary. The machine has a read-write head that scans cells and moves in left and right directions. The action of the machine is determined by the symbol in the cell being scanned and a table of transition rules that serve as the machine’s programming. Because of the infinite tape, a traditional Turing Machine has an infinite amount of time to compute any particular function or any number of functions. In the below example, each cell is either blank (B) or has a 1 written on it. These are the inputs to the machine. The possible outputs are:

• Halt: Do nothing.
• R: move one square to the right.
• L: move one square to the left.
• B: erase whatever is on the square.
• 1: erase whatever is on the square and print a ‘1.

The essential point to consider here is the nature of the states of the Turing machine. Each state can be defined exclusively in terms of its relations to the other states as well as inputs and outputs. State one, for example, is simply the state in which the machine, if it reads a B, writes a 1 and stays in that state, and in which, if it reads a 1, it moves one square to the right and goes into a different state. This is the functional definition of state one; it is its causal role in the overall system. The details of how it accomplishes what it accomplishes and of its material constitution are completely irrelevant.

According to machine-state functionalism, the nature of a mental state is just like the nature of the Turing machine states described above. If one can show the rational functioning and computing skills of these machines to be comparable to the rational functioning and computing skills of human beings, it follows that Turing machine behavior closely resembles that of human beings.[8] Therefore, it is not a particular physical-chemical composition responsible for the particular machine or mental state, it is the programming rules which produce the effects that are responsible. To put it another way, any rational preference is due to the rules being followed, not to the specific material composition of the agent.

Psycho-functionalism

A second form of functionalism is based on the rejection of behaviorist theories in psychology and their replacement with empirical cognitive models of the mind. This view is most closely associated with Jerry Fodor and Zenon Pylyshyn and has been labeled psycho-functionalism.

The fundamental idea of psycho-functionalism is that psychology is an irreducibly complex science and that the terms that we use to describe the entities and properties of the mind in our best psychological theories cannot be redefined in terms of simple behavioral dispositions, and further, that such a redefinition would not be desirable or salient were it achievable.

Psychofunctionalists view psychology as employing the same sorts of irreducibly teleological or purposive explanations as the biological sciences. Thus, for example, the function or role of the heart is to pump blood, that of the kidney is to filter it and to maintain certain chemical balances and so on — this is what accounts for the purposes of scientific explanation and taxonomy. There may be an infinite variety of physical realizations for all of the mechanisms, but what is important is only their role in the overall biological theory. In an analogous manner, the role of mental states, such as belief and desire, is determined by the functional or causal role that is designated for them within our best scientific psychological theory. If some mental state which is postulated by folk psychology (e.g. hysteria) is determined not to have any fundamental role in cognitive psychological explanation, then that particular state may be considered not to exist. On the other hand, if it turns out that there are states which theoretical cognitive psychology posits as necessary for explanation of human behavior but which are not foreseen by ordinary folk psychological language, then these entities or states exist.

Homuncular functionalism

Homuncular functionalism was developed largely by Daniel Dennett and has been advocated by William Lycan. It arose in response to the challenges that Ned Block’s China Brain (a.k.a. Chinese nation) and John Searle’s Chinese room thought experiments presented for the more traditional forms of functionalism.

In attempting to overcome the conceptual difficulties that arose from the idea of a nation full of Chinese people wired together, each person working as a single neuron to produce in the wired-together whole the functional mental states of an individual mind, many functionalists simply bit the bullet, so to speak, and argued that such a Chinese nation would indeed possess all of the qualitative and intentional properties of a mind; i.e. it would become a sort of systemic or collective mind with propositional attitudes and other mental characteristics.

Whatever the worth of this latter hypothesis, it was immediately objected that it entailed an unacceptable sort of mind-mind supervenience: the systemic mind which somehow emerged at the higher-level must necessarily supervene on the individual minds of each individual member of the Chinese nation, to stick to Block’s formulation. But this would seem to put into serious doubt, if not directly contradict, the fundamental idea of the supervenience thesis: there can be no change in the mental realm without some change in the underlying physical substratum. This can be easily seen if we label the set of mental facts that occur at the higher-level M1 and the set of mental facts that occur at the lower-level M2. Then M1 and M2 both supervene on the physical facts, but a change of M1 to M2 (say) could occur without any change in these facts.

Since mind-mind supervenience seemed to have become acceptable in functionalist circles, it seemed to some that the only way to resolve the puzzle was to postulate the existence of an entire hierarchical series of mind levels (analogous to homunculi) which became less and less sophisticated in terms of functional organization and physical composition all the way down to the level of the physico-mechanical neuron or group of neurons. The homunculi at each level, on this view, have authentic mental properties but become simpler and less intelligent as one works one’s way down the hierarchy.

In conclusion, functionalism is a philosophical theory that offers an alternative approach to understanding mental states, social systems, and even artificial intelligence. By focusing on the function or purpose of mental phenomena and their role within a broader framework, functionalism aims to provide a comprehensive and holistic explanation. Whether applied to the mind, society, or computational systems, functionalism offers valuable insights into the workings of complex systems and their diverse varieties.

References

• Block, Ned. (1996). “What is functionalism?” a revised version of the entry on functionalism in The Encyclopedia of Philosophy Supplement, Macmillan. (PDF online)
• Marr, D. (1982). Vision: A Computational Approach. San Francisco: Freeman & Co.
• Lewis, David. (1980). “Mad Pain and Martian Pain”. In Block (1980a) Vol. 1, pp. 216–222.
• Armstrong, D.M. (1968). A Materialistic Theory of the Mind. London: RKP.
• Putnam, Hilary. (1960). “Minds and Machines”. Reprinted in Putnam (1975a).
• Putnam, Hilary. (1967). “Psychological Predicates”. In Art, Mind, and Religion, W.H. Capitan and D.D. Merrill (eds.), pp. 37–48. (Later published as “The Nature of Mental States” in Putnam (1975a).
• Putnam, H. (1967). “The Mental Life of Some Machines,” in H.-N. Castaneda (Ed.), Intentionality, Minds, and Perception. Detroit, MI: Wayne State University Press, p. 183.
• Putnam, H. (1967). “The Mental Life of Some Machines,” in H.-N. Castaneda (Ed.), Intentionality, Minds, and Perception. Detroit, MI: Wayne State University Press, pp. 179–180.