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

Harnad responds

Powers's VTTT (Virtual TTT) is no TTT at all: just another TT, a symbols-only oracle. But if I assume that Powers does not mean to invoke Dyer's and McDermott's Cheshire cat with this example, but only the possibility that, in principle, a simulated robot in a simulated world, simulated by a sufficiently ingenious (very near omniscient) modeller, who had successfully anticipated and encoded everything that was relevant in both, could come up with the complete blueprint from which to build a real TTT-passing robot through virtual-world testing alone, then I don't disagree, though this seems just about as likely as Bringsjord's pongid poetry (and Powers seems to agree). But even then it would certainly not be just a matter of ``unplugging'' the virtual robot from its virtual world and ``replugging'' it into the real world (as Powers seems to suggest): if in doubt, try this first with virtual planets in a virtual cosmos.

And it would still only be the real TTT robot, successfully built from the principles learned from the VTTT, that was grounded. Virtual grounding is not grounding any more than virtual transduction is transduction. The causal connections between symbols and what they are interpretable as being about must be real. There is no way to break out of the symbolic circle through mere symbol/symbol connections.

Powers also seems to think Searle can simulate transduction the same way he can simulate symbol manipulation. I'd like to hear this spelled out in a concrete case, say, transducing photons. Short of using his own eyes as add-on peripherals (which would of course be begging the question -- see my reply to McDermott), the only way I can see to ``reconfigure'' Searle so as to be able to do this would seem to call for more radical forms of engineering than mere software!