Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
The Age Of Functionalism
If a mental state can be realized in more than one physical state, is the physical state important at all?
What is it that makes a physical state of the brain also a mental state? "Functionalists" had an answer: it's the “function” it performs in the life of the organism. This function will cause a behavior.
The physical state is not important in determining a mental state, but the function is. We call something a “thermometer” if it measures temperature, regardless of whether it is made of plastic or metal: it is the function, not the material, that determines what things are. Likewise, a mind is a mind if it has the function that a mind has, and it doesn't really matter what it is made of.
The "function" of something is a combination of the stimuli it processes, the operation it performs and the external behavior it causes.
Functionalism (basically introduced by Armstrong and Lewis) is really a special case of token-identity materialism in which a mental state is defined uniquely by the causal relation it bears over behavior and over other mental states. Mental states express, ultimately, causal relations (the occurring of something causes something else to take place). In other words, they ultimately have a function. Never mind what they are made of: mental states have a function and that is what matters.
A consequence of this approach is that a mind doesn’t necessarily require a brain: anything that can play the same function is a mind too. Mental states are defined by their function, and they may as well be implemented in a computer or a brain. As a matter of fact, by using a technique inspired by the British mathematician Frank Ramsey, it is possible to translate every sentence containing "unscientific" psychological terms (such as "believe", "desire", etc.) into a more formal sentence (akin to sentences of predicate logic) which only contains causal relations. The mind is simply the location at which these causal relations are carried out.
Of course, the difference between functionalists and behaviorists is not so clear cut. Basically, behaviorists refused to deal with mental states and focused on behavior, whereas functionalists said that mental states are such because they cause behavior. Functionalism does not deny the existence of mind, actually it extends the possible realizations of mind in nature (it doesn't have to be a brain).
Functionalism has an advantage over materialism: there is evidence that different neural circuits cause the same mental states (different people with different brains feel the same emotions, the same person with a changing brain feels the same emotions, a damaged brain tends to repair itself to perform the same chores it was doing before), but materialism entails that a mental state is a direct consequence of a physical state, which could be meant to signify that two different physical states yield two different mental states. Functionalism allows for "multiple realization". Strictly speaking, it doesn't even require that the mental state be realized in a brain: functionalism is only concerned with the "function", not with the thing that performs the function.
Since functions must be carried out by a physical entity, functionalism implied some kind of materialism. David Lewis explicitly married the two, materialism and functionalism: every mental state is a physical state, and every mental state is a functional state. The marriage of the two solved two classes of popular paradoxes, the "mad pain" paradox (what if a human was born who is made of flesh like everybody else but his reaction to the feeling of pain is completely different?) and the "android pain" paradox (what if a being made of different stuff reacted to pain the same way humans do?)
The whole debate on one or two substances is meaningless: what is relevant is the function, not the substance. A mind can be "implemented" in whatever number of substances, as long as it performs the function of a mind.
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