Functionalism (philosophy of mind): Difference between revisions

Philosophical position

In the philosophy of mind, functionalism is the thesis that each and every mental state (for example, the state of having a belief, of having a desire, or of being in pain) is constituted solely by its functional role, which means its causal relation to other mental states, sensory inputs, and behavioral outputs.^[1] Functionalism developed largely as an alternative to the identity theory of mind and behaviorism.

Functionalism is a theoretical level between the physical implementation and behavioral output.^[2] Therefore, it is different from its predecessors of Cartesian dualism (advocating independent mental and physical substances) and Skinnerian behaviorism and physicalism (declaring only physical substances) because it is only concerned with the effective functions of the brain, through its organization or its “software programs”.

Since a mental state is identified by a functional role, it is said to be realized on multiple levels; in other words, it is able to be manifested in various systems, even perhaps computers, so long as the system performs the appropriate functions. While a computer’s program performs the functions via computations on inputs to give outputs, implemented via its electronic substrate, a brain performs the functions via its biological operation and stimulus responses.

Multiple realizability[edit]

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) (Levin, § 3.4), as they are called, were most notably developed by David Lewis^[3] and David Malet Armstrong.^[4] 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^[5][6] 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.

Machine-state functionalism[edit]

The broad position of “functionalism” can be articulated in many different varieties. The first formulation of a functionalist theory of mind was put forth by Hilary Putnam^[5][6] in the 1960s. This formulation, which is now called machine-state functionalism, or just machine functionalism, was inspired by the analogies which Putnam and others noted between the mind and the theoretical “machines” or computers capable of computing any given algorithm which were developed by Alan Turing (called Turing machines). Putnam himself, by the mid-1970s, had begun questioning this position. The beginning of his opposition to machine-state functionalism can be read about in his Twin Earth thought experiment.

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…