Functionalism and Materialism

Functionalism and Materialism

We have been told that mental states admit of multiple realization; this is the heart of the functionalist doctrine. Keep the function while letting the matter vary and you keep the mental state. The idea is not without merit; function must surely be part of what matters to mind. Pain could not have the function of pleasure, or thought have the function of emotion; but they could be embodied in a different material substrate, so long as they are embodied in some material substrate. Thus, functionalism keeps a foot in the materialist camp, while not identifying mind with matter. But is it really clear that the substrate must be material? Could an immaterial substance realize the same function? Is that inconceivable? Can it be ruled out a priori that an immaterial stuff could exemplify the same functional description as a material stuff? If such a stuff exists, it will have causal properties, and these will exhibit a certain pattern, i.e., be elicited by certain inputs and produce certain outputs. The idea of functionalism is hospitable to an immaterialist interpretation; the two ideas are consistent. So, mind is not materially realized by definition; if it is so realized, this will be de facto not de jure. Functionalism is not essentially a materialist doctrine. Descartes could be a firm functionalist. He might even hold that only an immaterial substance could have the functional properties of a mental state—matter being too gross and geometrically inclined. Dualistic functionalism is both consistent and metaphysically attractive (in some respects). It should be added to the menu of options.

But there is a more radical possibility to consider, namely that so-called materialism is itself a form of functionalism. Take the classical identity theory: pain is identical to C-fiber firing. Are C-fibers themselves intrinsically material—are they necessarily made of matter? Well, what are C-fibers? They are standardly defined by three types of property: function, structure, and mechanism. Their function is to transmit sensations of pain, as a result of stimuli of certain kinds (thermal, chemical, mechanical). Their structure is described as unmyelinated (lacking an insulating sheath), thin, and distributed all over the body: this is their physical geometry. Their mechanism of action is to release chemicals (neuropeptides) which bind to receptors and trigger electrical signals. There is no mention here of material composition; nothing says that these functional-structural-mechanistic entities must be made of matter, still less the kind of matter that exists in our universe or our sector of the universe. Couldn’t these fibers be multiply realized in different possible worlds, or in different parts of the actual world? Just as spoons may be made of metal, wood, or plastic, couldn’t C-fibers be made of different kinds of stuff, actually or possibly. Function, structure, and causal mechanism don’t tie things down to a specific constituting stuff. Indeed, can it be ruled out a priori that C-fibers could be realized in immaterial stuff? The function could be, and even the structure might admit of morphological similarity—thin and slow. Does something have to be made of matter in order to be thin?[1]What about thin air? Or a thin argument? Certainly, atomic matter is not required for thinness. Wouldn’t something still be a C-fiber if it had the same function as our C-fibers and had a structure like ours? And couldn’t C-fibers exist and be quite thick? As to mechanism, we just need certain causal powers, and these might reside in something other than our local matter. God could have made the universe with a different universal stuff and yet preserved function, structure, and mechanism; so, C-fibers are not identical to strands of matter as they exist here. There is no necessity about the composition relation. Do we even have to suppose that C-fibers are necessarily made of quarks? The natural kind in question is closely tied to function and structure not to material composition (or immaterial). If so, mind-brain identity is not a form of materialism, strictly speaking (type identity). It doesn’t identify the mind with the material substance of the universe, because the brain isn’t defined by such a substance. We should be functionalists about the brain: neurons are functionally (and structurally) defined. The real essence of this natural biological kind is located at a higher level than the underlying matter; its individuation proceeds at the functional-structural level not at the basic compositional level. Immaterial stuff will do just as well as material stuff so long as it works the same way and has a similar shape (abstractly understood). So, there is nothing in the definition of the mind-brain identity theory to tie the mind to the underlying stuff of the brain. In general, cells are defined (constituted) by their function and structure (and how they work) not by their raw material. In another part of the universe, we might come across aliens who share our cellular make-up but not our material composition (dark matter not visible matter, quorks not quarks). Hence, histological functionalism. It could be that no natural kind in the universe is necessarily tied to its actual constituent matter (except matter itself); all individuation of natural kinds proceeds at a higher level. Materialism is false of everything! Everything is really functional, i.e., individuated independently of the basic stuff. Everything can be multiply realized in principle. It might still be true that pain is identical to C-fiber firing, but C-fibers themselves are not material things; in Martians the C-fibers might be made of some strange goo like nothing we have ever experienced, though they have roughly the same form and do the same job as our C-fibers. It would be like going to another planet and finding that the cutlery is made of plastic while we had never invented the stuff. Functionalism runs deep.[2]

[1] A line in space could be described as thin without being material, or an ideal abstract line. What about a narrow band of light? Also, it is not obvious that an immaterial substance has to be without volume and shape (pace Descartes): couldn’t there be a volume of immaterial stuff that is divisible into spatial parts? It might have a geometry without being made of hard bits (like a field of force). It might be fibrous (filamentary, threadlike) but ethereal.

[2] Given that we need to add structure to function to deal with “physical” things, we might need to rechristen functionalism as structuralism, applying that notion to the structure of the causal relations in which the kind is involved (the causal network). We need a unifying concept to tie together shape and action, since these are naturally connected.