Instituut voor Taal- en Kennistechnologie
Institute for Language Technology and Artificial Intelligence

Harnad responds

Dyer thinks thinking corresponds to a level of organization in a computer, the differences among the ways this same organization could be implemented being irrelevant. The question I keep asking those who adopt this position is: Why on earth should one believe this? Look at the evidence for every other kind of example one could think of: Compare the respective virtual and real counterparts of planetary systems, fluids, electrons, furnaces, planes, and cells, and consider whether, respectively, movement, liquidity, charge, heat, flight and life might be an ``organizational'' property that they share. I see absolutely no reason to think so, so why think so of thought?

But, of course, it's possible, because unlike the observable properties I singled out above, thought is unobservable (with one notable exception, which I will return to). So perhaps thought can be correctly attributed to a virtual mind the same way quarks or superstrings (likewise unobservable) can be attributed to (real) matter. Who's to be the wiser?

The first intuition to consult would be whether those of us who are not willing to attribute motion in any sense of the word to a virtual universe would be more willing to attribute quarks to it. I wouldn't; at best, there would just be squiggles and squoggles that were interpretable as matter, which was in turn interpretable as a manifestation of quarks: and virtual quarks, though just as unobservable as real quarks, do not thereby become real! Ditto, I would say, for virtual thoughts.

But again, it still seems possible (that's part of the equivocality of unobservables: they're much more hospitable to modal fantasies than observables are). This is of course the place to invoke the one exception to the unobservability of thought: The thinker of the thought. he of course knows whether our attribution is correct (or not, although in that case no knowing is going on). And that is precisely the observation-point where Searle cleverly positions himself. For the thesis that thinking is just computation, i.e., just implementation-independent symbol manipulation, with the thinking necessarily ``supervening'' on every implementation of the symbol system, is exquisitely vulnerable to the Chinese Room Argument. And this has nothing to do with ``levels.'' Whether Searle manipulates the symbols in a higher-level programming language or all the way down at the binary machine code level, the question is: Is anyone home in there, understanding? Searle says ``no''; the symbols he manipulates are systematically interpretable as saying ``yes.'' Whom should you believe?

I, for one, see no difference between Searle's implementation of the TT-passing computer and Searle's implementation of the planetary system simulator. In the latter case Searle also manipulates symbols that are systematically interpretable as motion, yet there is no motion in either case. What is the grounds for the special dispensation in the case of the mind simulation? Are we in the habit of thinking that merely memorizing and manipulating a bunch of meaningless symbols gives birth to a second mind?

As I've said before, we risk being drawn into the hermeneutic circle here (Harnad 1990c); such is the power of symbolic oracles that simulate pen-pals instead of planets: We can't resist the interpretation. But a step back (and out of the circle) should remind us that we're just dealing with meaningless squiggles and squoggles in both cases. Does Dyer really think that my readiness to believe that

is all that much more counterintuitive than the belief that And although there is no problem with a real body with a real mind and real TTT capacity, like mine, whether it is interacting with a real or a virtual world, and likewise no problem with a real robot with real TTT capacity (and hence, by my lights, a real mind), whether it is interacting with a real or virtual world, there is definitely a problem if you try to make the equation virtual on both ends -- a virtual robot in a virtual world. For then all you have left is the Cheshire cat's smile and a bunch of squiggles and squoggles. It is clear that it is only the (real!) sensorimotor transducer surface and the real energy hitting it that can keep such a system out of the hermeneutic circle.

I, by the way, do not define mind at all (we all know what it's like to be one) and insist only on real TTT-capacity, no more, no less. I think the science (engineering, actually) ends there, and the only thing left is trust.