ray@BOEING.COM (Ray Allis) (06/18/87)
I have enjoyed the ailist's tone of rarified intellectual inquiry, but lately I have begun to think the form of the question "What is the solution to the Symbol Grounding Problem" has unduly influenced the content of the answer, as in "How many angels can dance on the head of a pin?" You are solemnly discussing angels and pinheads. There is no "Symbol Grounding Problem"; the things are *not* grounded. The only relationship a symbol has with anything is that the physical effects (electrical and chemical) of its perception in the brain of a perceiver co-exist with the physical effects of other perceptions, and are consequently associated in that individual's brain, and therefore mind. It happens when we direct our baby's attention at a bovine and clearly enunciate "COW". There is no more "physical invertibility" in that case than there is between you and your name, and there is no other physical relationship. And, as we computer hackers are wont to say, "That's a feature, not a bug". It means we can and do "think" about things and relationships which may not "exist". (BTW, it's even better! You are right now using second-level symbols. The visual patterns you are perceiving on paper or on a display screen are symbols for sounds, which in turn are symbols for experiences.) Last year's discussion of the definitions of "analog" and "digital" are relevant to the present topic. In the paragraph above, the electrical and chemical effects in the observer's brain are an *analogy* (we hypothesize) of external "reality". These events are *determined* (we believe) by that reality, i.e., for each external situation there is one and only one electro-chemical state of the observer's brain. Now, the brain effects appear pretty abstracted, or attenuated, so "complete invertibility" is unlikely, but if we can devise a fancy enough brain, may be approachable. No such deterministic relationship holds between external "reality" and symbols. As I noted above, symbols are related to their referents by totally arbitrary association. Thus, there is nothing subtle about the distinction between "analog" and "digital"; they are two profoundly different things. The "digital" side of an A/D relationship is *symbolic*. The relationship (we humans create) between a symbol and a quantity is wholly arbitrary. The value here is that we can use *deductive* relationships in our manipulation of quantities, rather than, say, pouring water back and forth among a set of containers to balance our bank account. I am one of those convinced by such considerations that purely symbolic means, which includes most everything we do on digital computers, are *insufficient in principle* to duplicate human behavior. And I have some ideas about the additional things we need to investigate. (By the way, whose behavior are we to duplicate? Ghengis Khan? William Shakespeare? Joe Sixpack? All of the above in one device? The Total Turing Test is just academic obfuscation of "If it walks like a duck, and quacks like A duck ...").