Functionalism

Functionalism in philosophy of mind is the theory that functions are dispositive—activities, roles, results, outputs—mediums are not. What's critical is how mental states work, not in what substrates mental states are found (Levin, 2023). Mental states are not dependent on their internal constitutions, what they are, but rather only on their outputs or roles, what they do. As long as the functions (activities) are conducive to creating consciousness, it does not matter whether the substrates are neural tissue or computer chips or any form of matter that can instantiate information.

Ned Block defines functionalism as the theory that “mental states are constituted by their causal relations to one another and to sensory inputs and behavioral outputs.” Functionalism can be appreciated, he says, by attending to “artifact concepts like carburetor and biological concepts like kidney. What it is for something to be a carburetor is for it to mix fuel and air in an internal combustion engine—carburetor is a functional concept. In the case of the kidney, the scientific concept is functional—defined in terms of a role in filtering the blood and maintaining certain chemical balances” (Block, 1980, 2007b).

Block gives the functionalist answer to the perennial question, “What are mental states?”, stating simply that “mental states are functional states.” The significance of this simple identity is precisely this simple identity. Thus, he says, “theses of metaphysical functionalism are sometimes described as functional state identity theses” (Block, 1980, 2007b).

Functionalism and Physicalism

Block explores the relationship between functionalism and reductive physicalism. “The first step in a reductive physicalist enterprise,” he says, “is to functionally characterize the property to be reduced and the second step is to find the physical property that fills the functional role. Reductive physicalism is true for the mind if both steps can always be carried out.”

Block makes the at-first counterintuitive claim that reductive physicalism and functionalism are “incompatible rivals,” explaining that when understood as metaphysical theses, “appearances to the contrary stem from failure to sufficiently appreciate the upshot of the difference between metaphysics and ontology”—in that functionalism is agnostic on the existence of nonphysical substances (Block, 2008).

David Chalmers uses a silicon-chip-replacement thought experiment to support a functional approach to consciousness.^[1] “When experience arises from a physical system,” he says, “it does so in virtue of the system's functional organization.” The thought experiment replaces brain neurons with microchips that can duplicate 100% of the neuron's functions, and to do so slowly, even one by one. (That such technology is fiendishly complex is irrelevant.) The question is, what happens to one's conscious experience, one's qualia? Would it gradually wink or fade out? Chalmers says no: the conscious experience, the qualia, would not change—there would be no difference at all.

This result would support Chalmers's “principle of organizational invariance, holding that experience is invariant across systems with the same fine-grained functional organization” (Chalmers, 1995b). Not everyone agrees, of course (Block, 2023; Van Heuveln et al., 1998).

Computational and Applied Functionalism

Computational functionalism goes further and commits to the thesis that performing computations of a particular, natural, and likely discoverable kind is both necessary and sufficient for consciousness in general and ultimately for human-level consciousness (and perhaps for speculative higher forms of consciousness). Whether consciousness is indeed computational elicits probative and profound debate (Penrose, 1996, 1999).

Functionalism with respect to consciousness is more an overarching principle, a way of thinking, than a proffered model, a claimed explanation on its own. Functionalism can apply in many Materialist Theories and it is often assumed as an a priori premise.

Functionalism is the theoretical foundation of “virtual immortality,” the theory that the fullness of our mental selves can be uploaded with first-person perfection to non-biological media so that when our mortal bodies die, our mental selves will live on (Kuhn, 2016a). (See “Virtual Immortality.”)

Footnote

[1]. Ned Block says that the example used in the fading qualia argument may derive from John Haugeland (1980), but that “the best version is that of Chalmers (1995)” (Block, 2023, p. 451).