David J. Chalmers
From: email@example.com (David Chalmers)
Subject: Re: Two Materialisms (Was: Re: Strong AI and Panpsychism)
Date: Thu, 30 Jan 92 03:50:35 GMT
B Chandrasekaran writes:
It appears that there are three realms: the realm of matter, the realm of representations, and the realm of qualia/intentions/consciousness, not just two: matter and consciousness.
I like this distinction, although I think there might more naturally be four realms to distinguish.
On the relations between the various realms:
The functional realm is uncontroversially reducible to the physical realm.
Modern cognitive science holds that the representational realm is reducible to the functional realm, and I agree, although some, e.g. Searle, disagree, holding that it is only reducible to the physical realm, and no doubt you could find some who don't accept even that (e.g. people who hold that representation is dependent on consciousness, and that consciousness isn't reducible to the physical).
Consciousness is where things get tricky. Some people think that consciousness is reducible to representation (e.g. Dennett, Harman, and possibly many cognitive scientists, though cognitive scientists don't talk much about consciousness). Many more think that consciousness is reducible to function (Lewis, Armstrong, McDermott, most functionalists, etc), but not necessarily to representation. Still others (notably Searle) thinks that consciousness is reducible to the physical, but not to the other realms. Incidentally Searle also differs from most others in holding that representation is itself dependent on consciousness.
Penrose may in some strange sense hold that consciousness is reducible to function, but believes that the right function can only be realized through quantum effects (but he's so vague that one can't know). A Cartesian dualist like Eccles doesn't think that consciousness is reducible to physics, but might just possibly think that it's reducible to function that happens to be realized by ghostly spirits.
Then there are people like me who can't see how consciousness could be reduced to physics (and consequently, to function or representation either), though it would be nice if somehow it could be.
Finally there are people who don't think that consciousness really exists as a phenomenon worth talking about (perhaps Minsky, and Dennett on some days), so there's no point reducing it to anything. Personally I think that apart from the strong anti-reductionist position, this is the only position that's at all tenable, although it does seem to be prima facie implausible.
In my paper on connectionism in AI Magazine a few years ago, I argued that part of the excitement surrounding connectionism in its early stages was the claim of skipping the second realm, i.e., it was more directly physical and not representational. Most connectionists quickly abandoned this notion, since they came to see that it was every bit as representational as the symbolic systems, only different. Edelman seems to think he is offering a purely physicalist account, without any representational intervention, but I think there is representation there nevertheless.
I think that the enlightened connectionist position has always been that the cognitive realm (which is more or less the representational realm) is reducible to the functional realm - you don't find many connectionists talking directly in terms of physics. It's just that they want to reduce it to functional mechanisms quite different from those used by traditional AI and cognitive science.
To be strictly accurate I should probably introduce the cognitive realm as a fifth realm - i.e. the realm concerned with the explanation of behaviour - and not beg any questions about the identification of this with the representational realm. Some cognitive scientists want to skip the representational realm altogether, and go straight from the cognitive to the functional (e.g. Brooks, Freeman, the Churchlands on some days, and possibly some of the connectionists you mention). Most cognitive scientists, by contrast, take it for granted that cognitive explanation will be representational explanation; or more accurately, jointly representational and functional explanation. A few people (Fodor, Pylyshyn, ...) might hold that one can perform the reduction to the representational realm fully before a reduction to the functional realm, but even these people will rely on nonrepresentational functional explanations for some cognitive phenomena, e.g. perception. But I'd better stop now. The space of realms is getting cluttered.