Functionalism (philosophy of mind)

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.

The beginning of his opposition to machine-state functionalism can be read about in his Twin Earth thought experiment.

To put it another way, any rational preference is due to the rules being followed, not to the specific material composition of the agent.

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.

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.

The basic idea of analytic functionalism is that theoretical terms are implicitly defined by the theories in whose formulation they occur and not by intrinsic properties of the phonemes they comprise.

Such terms are subject to conceptual analyses which take something like the following form: For example, the state of pain is caused by sitting on a tack and causes loud cries, and higher order mental states of anger and resentment directed at the careless person who left a tack lying around.

These sorts of functional definitions in terms of causal roles are claimed to be analytic and a priori truths about the submental states and the (largely fictitious) propositional attitudes they describe.

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.

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.

Functionalism is fundamentally what Ned Block has called a broadly metaphysical thesis as opposed to a narrowly ontological one.

Ned Block[18] argues against the functionalist proposal of multiple realizability, where hardware implementation is irrelevant because only the functional level is important.

[21] The Chinese room argument by John Searle[22] is a direct attack on the claim that thought can be represented as a set of functions.

The thought experiment asserts that it is possible to mimic intelligent action without any interpretation or understanding through the use of a purely functional system.

According to Searle, it would be absurd to claim that the English speaker inside knows Chinese simply based on these syntactic processes.

This thought experiment attempts to show that systems which operate merely on syntactic processes (inputs and outputs, based on algorithms) cannot realize any semantics (meaning) or intentionality (aboutness).

One common response to Searle's thought experiment is that there is a form of mental activity going on at a higher level than the man, and that the whole system needs to be considered.

Even if he internalized all the rules and performed the operations in his mind, he would still be manipulating symbols without understanding their meaning, according to Searle.

Some critics consider that this symbol-manipulating subsystem of the brain can be viewed as a kind of separate, virtual mind, which would understand Chinese.

[18][24] This thought experiment involves supposing that there is a person, call her Jane, that is born with a condition which makes her see the opposite spectrum of light that is normally perceived.

For example, it implies that a silicon chip that is functionally isomorphic to a brain will have the same perception of the color red, given the same sensory inputs.

It is a reductio ad absurdum argument that starts by supposing that two such systems have different qualia in the same situation.

Most defenders of functionalism initially responded to this argument by attempting to maintain a sharp distinction between internal and external content.

According to Ned Block, if functionalism is to avoid the chauvinism of type-physicalism, it becomes overly liberal in "ascribing mental properties to things that do not in fact have them".

Peter Godfrey-Smith has argued further[34] that such formulations can still be reduced to triviality if they accept a somewhat innocent-seeming additional assumption.