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hilary _minds and machines

hilary _minds and machines - 18 Minds and machines" The...

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Unformatted text preview: 18 Minds and machines" The various issues and puzzles that make up the traditional mind—body problem are wholly linguistic and logical in character: whatever few empirical ‘facts’ there may be in this area support one view as much as another. I do not hope to establish this contention in this paper, but I hope to do something toward rendering it more plausible. Specifically, I shall try to show that all of the issues arise in connection with any computing system capable of answering questions about its own structure, and have thus nothing to do with the unique nature (if it is unique) of human subjective experience. * To illustrate the sort of thing that is meant: one kind of puzzle that is sometimes discussed in connection with the ‘mind—body problem’ is the puzzle of privacy. The question ‘How do I know I have a pain?’ is a deviant-f (‘logically odd’) question. The question ‘How do I know Smith has a pain?’ is not all at deviant. The difference can also be mirrored in impersonal questions: ‘How does anyone ever know he himself has a pain?’ is deviant; ‘How does anyone ever know that some— one else is in pain?’ is non-deviant. I shall show that the difference in status between the last two questions is mirrored in the case of machines: if T is a Turing machine (see below), «the question ‘How does T ascertain that it is in state A?’ is, as we shall see, ‘logically odd’ with a vengeance; but if T is capable of investigating its neighbor machine T' (say, T has electronic ‘sense—organs’ which ‘scan’ T’), the question ‘How does T ascertain that T’ is in state A?’ is not at all odd. Another question connected with the ‘mind—body problem’ is the question whether or not it is ever permissible to identify mental events and physical events. Of course, I do not claim that this question arises for Turing machines, but I do claim that it is possible to construct a logical analogue for this question that does arise, and that all of the question of ‘mind—body identity’ can be mirrored in terms of the analogue. * First published in Sidney Hook (ed.) Dimensions of Mind (New York, 1960)- Reprinted by permission of New York University Press. 1- By a ‘deviant’ utterance is here meant one that deviates from a semantical regularity (in the appropriate natural language). The term is taken from Ziff, 1960. 362 MINDS AND MACHINES To obtain such an analogue, let us identify a scientific theory with a ‘partially-interpreted calculus’ in the sense of Carnapt. Then we can perfectly well imagine a Turing machine which generates theories, tests them (assuming that it is possible to ‘mechanize’ inductive logic to some degree), and ‘accepts’ theories which satisfy certain criteria (e.g. pre- dictive success). In particular, if the machine has electronic ‘sense organs’ which enable it to ‘scan’ itself while it is in operation, it may formulate theories concerning its own structure and Subject them to test. Suppose the machine is in a given state (say, ‘state A’) when, and only when, flip-flop 36 is on. Then this statement: ‘I am in state A when, and only when, flip—flop 36 is on’, may be one of the theoretical principles concerning its own structure accepted by the machine. Here ‘I am in state A’ is, of course, ‘observation language’ for the machine, while ‘flip—flop 36 is on’ is a ‘theoretical expression’ which is partially interpreted in terms of ‘observables’ (if the machine’s ‘sense organs report by printing symbols on the machine’s input tape, the ‘observ- ables’ in terms of which the machine would give a partial operational definition of ‘flip—flop 36 being on’ would be of the form ‘symbol # so—and—so appearing on the input tape’). Now all of the usual considera- tions for and against mind—body identification can be paralleled by considerations for and against saying that state A is in fact identical with flip-flop 36 being on. Corresponding to Occamist arguments for ‘identify’ in the one case are Occamist arguments for identity in the other. And the usual argu— ment for dualism in the mind—body case can be paralleled in the other as follows: for the machine, ‘state A’ is directly observable; on the other hand, ‘flip—flops’ are something it knows about only via highly—sophisti— cated inferences e How could two things so different possibly be the same? This last argument can be put into a form which makes it appear somewhat stronger. The proposition: (1) I am in state A if, and only if, flip—flop 36 is on, is clearly a ‘synthetic’ proposition for the machine. For instance, the machine might be in state A and its sense organs might report that flip— flop 36 was not on. In such a case the machine would have to make a methodological ‘choice’ — namely, to give up (I) or to conclude that it had made an ‘observational error’ (just as a human scientist would be confronted with similar methodological choices in studying his own th. ~Carnap 1953 and 1956. This model of a scientific theory is too oversimplified to be of much general utility, in my opinion: however, the oversimplificztions do not affect the present argument. ’ 363 MIND, LANGUAGE AND REALITY psychophysical correlations). And just as philosophers have argued from the synthetic nature of the proposition: (2) I am in pain if, and only if, my C-fibers are stimulated, to the conclusion that the properties (or ‘states’ or ‘events’) being in pain, and having C-fibers stimulated, cannot possibly be the same (otherwise (2) would be analytic, or so the argument runs); so one should be able to conclude from the fact that (I) is synthetic that the two properties (or ‘states’ or ‘even.ts’) — being in state A and having flip- flop 36 on — cannot possibly be the same! It is instructive to note that the traditional argument for dualism is not at all a conclusion from ‘the raw data of direct experience’ (as is shown by the fact that it applies just as well to non-sentient machines), but a highly complicated bit of reasoning which depends on (a) the reification of universalsf (e.g. ‘properties’, ‘states’, ‘events’); and on (b) a sharp analytic—synthetic distinction. I may be accused of advocating a ‘mechanistic’ world—view in pressing the present analogy. If this means that I am supposed to hold that machines think,I on the one hand, or that human beings are machines, on the other, the charge is false. If there is some version of mechanism sophisticated enough to avoid these errors, very likely the considerations in this paper support it.§ 1. Turing Machines The present paper will require the notion of a Turing machine” which will now be explained. Briefly, a Turing machine is a device with aTinite number of internal configurations, each of which involves the machine’s being in one of a finite number of statesfll and the machine’s scanning a tape on which certain symbols appear. 1- This point was made by Quine in Quine, 1957. I Cf. Ziff’s paper (1959) and the reply (1959) by Smart. Ziff has informed me that by a ‘robot’ he did not have in mind a ‘learning machine’ of the kind envisaged by Smart, and he would agree that the considerations brought forward in his paper would not necessarily apply to such a machine (if it can properly be classed as a ‘machine’ at all). On the question of whether ‘this machine thinks (feels, etc.) ’ is deviant or not, it is necessary to keep in mind both the point raised by Ziff (that the important question is not Whether or not the utterance is deviant, but whether or not it is deviant for non- trivial reasons), and also the ‘diachronic—synchronic’ distinction discussed in section 5 of the present paper. . § In particular, I am sympathetic with the general standpoint taken by Smart 10 (1959b) and (1959c). However, see the linguistic considerations in section 5. II For further details, cf. Davis, 1958 and Kleene, 1952. 1] This terminology is taken from Kleenc, 1952, and differs from that of Davis and Turing. 364 MINDS AND MACHINES The machine’s tape is divided into separate squares, thus- lJ l ill on each of which a symbol (from a fixed finite alphabet) may be printed Also the machine has a ‘scanner’ which ‘scans’ one square of the ta e at a time. Finally, the machine has a printing mechanism which ma (1:1) erase the symbol which appears on the square being scanned and, (b) print some other symbol (from the machine’s alphabet) on that square AnyTurmg machine is completely described by a machine table- which Is constructed as follows: the rows of the table correspond td letters of the alphabet (including the ‘null’ letter, i.e. blank space) while the columns correspond to states A, B, C, etc. In each square’ there appears an ‘instruction’, e.g. ‘s5L A’, ‘s7C B’, ‘33R C’. These instruc— tions are read as follows: ‘s5L A’ means ‘print the symbol :5 on the square you are now scanning (after erasing whatever symbol it now contains), and proceed to scan the square immediately to the left of the one you have just been scanning; also, shift into state A.’ The other instructions are similarly interpreted (‘R’ m immediately to the right’, while ‘C’ means eans ‘scan the square , . . center’, i.e. continue scanning the same square). The following is a sample machine table: A B C D (51) I isA leB 53LD x1 CD (32) + leB 52C D s2LD S2CD blank (53) space s3 CD s3RC 53LD 33 CD The machine described by this table is intended to function as ,fOHOVYS’. the machine is started in state A. On the tape there appears a sum (in unary notion) to be ‘worked out’, e.g. ‘11 + 111." The machine is initially scanning the first ‘ 1 ’. The machine proceeds to work out’ the sum (essentially by replacing the plus sign by a I and then gOing back and erasing the first 1). Thus if the ‘input’ was I IiI + ‘11111 the machine would ‘print out’IIIIIIIII, and then go into the rest state’ (state D). A ‘machine table’ describes a machine if the machine has internal states corresponding to the columns of the table, and if it ‘obeys’ the instruction in. the table in the following sense: when it is scanning a square on which a symbol 3, appears and it is in, say, state B that it carries. out the ‘instruction’ in the appropriate row and column of the table (in this case, column B and row 3,). Any machine that is described by a machine table of the sort just exemplified is a Turing machine. 365 MIND, LANGUAGE AND REALITY The notion of a Turing machine is also subject to generalizationj‘ in various ways — for example, one may suppose that the machine has a second tape (an ‘input tape’) on which additional information may be printed by an operator in the course of a computation. In the sequel we shall make use of this generalization (with electronic ‘sense organs’ taking the place of the ‘operator’). It should be remarked that Turing machines are able in principle to do anything that any computing machine (of whichever kind) can dol It has sometimes been cont‘etided (e.g. by Nagel and Newman in their book Godel’s Proof) that ‘the theorem [i.e. Godel’s theorem] does indicate that the structure and power of the human mind are far more complex and subtle than any non-living machine yet envisaged’ (p. 10), and hence that a Turing machine cannot serve as a model for the human mind, but this is simply a mistake. Let T be a Turing machine which ‘represents’ me in the sense that T can prove just the mathematical statements I can prove. iT hen the argu— ment (Nagel and Newman give no argument, but I assume they must have this one in mind) Ts that by using Godel’s technique I can discover a proposition that T cannot prove, and moreover I can prove this proposition. This refutes the assumption that T ‘represents’ me, hence I am not a Turing machine. The fallacy is a misapplication of Godel’s theorem, pure and simple. Given an arbitrary machine T, all I can do is find a proposition U such that I can prove: (3) If T is consistent, Uis true, where U is undecidable by T if T is in fact consistent. However, T can perfectly well prove (3) too! And the statement U, which T cannot prove (assuming consistency), I cannot prove either (unless I can prove that T is consistent, which is unlikely if T is very complicated)! 2. Privacy Let us suppose that a Turing machine T is constructed to do the following. A number, say ‘3000’ is printed on T’s tape and T is started in T’s ‘initial state’. Thereupon T computes the 3oooth (or whatever the given number was) digit in the decimal expansion of 7r, prints this digit on its tape, and goes into the ‘rest state’ (i.e. turns itself off). 1" This generalization is made in Davis, 1958, where it is employed in defining relative recursiveness. I This statement is a form of Church’s thesis (that rccursivcncss equals effective computability). 366 MINDS AND MACHINES Clearly the question ‘How does T “ascertain” [or “ compute ” or “work ’) o n n 4 ’ out ] the 3oooth digit in the deCimal expansion of 77?’ is a sensible question. And the answer might well be a complicated one. In fact, ‘ an answer would probably involve three distinguishable constituents: ('1). A description of the sequence of states through which T passed in arrivmg at the answer, and of the appearance of the tape at each stage in the computation. (ii) A description of the rules under which T operated (these are given by the ‘machine table’ for T). (iii) An explanation of the rationale of the entire procedure. ‘ Now let us suppose that someone voices the following objection: In order to perform the computation just described, T must pass through states A, B, C, etc. But how can T ascertain that it is in states A, B, C, etc?’ .It is clear that this is a silly objection. But what makes it silly? For one thing, the ‘logical description’ (machine table) of the machine describes the state only in terms of their relations to each other and to what appears on the tape. The ‘physical realization’ of the machine is immaterial, so long as there are distinct states A, B, C, etc., and they succeed each other as specified in the machine table. Thus one can answer a question such as ‘How does T ascertain that X?’ (or ‘compute X ’, etc.) only in the sense of describing the sequence of states through which T must pass in ascertaining that X (computing, X etc.), the rules obeyed, etc. But there is no ‘sequence of states’ through which T must pass to be in a single state! IIndeed, suppose there were — suppose T could not be in state A Without first ascertaining that it was in state A (by first passing through a sequence of other states). Clearly a Vicious regress would be involved. And one I‘breaks’ the regress simply by noting that the machine, in ascertaining the 3oooth digit in 7r, passes through its states — but it need not in any significant sense ‘ascertain’ that it is passing through them. Note the analogy to a fallacy in traditional epistemology: the fallacy of supposing that to know thatp (wherep is any proposition) one must first know that 91, (12, etc. (where ql, (12, etc., are appropriate other pro- posmons). This leads either to an ‘infinite regress’ or to the dubious move of inventing a special class of ‘protocol’ propositions. The resolution of the fallacy is also analogous to the machine case. Suppose that on the basis of sense experiences E1, E2, etc., Iknow that there is a chair in the room. It does not follow that I verbalized (or even could have verbalized) E1, E2, etc., nor that I remember E1, E2, etc., nor 367 MIND, LANGUAGE AND REALITY even that I ‘mentally classified’ (‘attended to’, etc.) sense experiences E1, E2, etc., when I had them. In short, it is necessary to have sense experiences, but not to know (or even notice) what sense experiences one is having, in order to have certain kinds of knowledge. Let us modify our case, however, by supposing that whenever the machine is in one particular state (say, ‘state A’) it prints the words ‘I am in state A’. Then someone might grant that the machine does not in general ascertain what state it is in, but might say in the case of state A (after the machine printed ‘I am in state A’): ‘The machine ascertained that it was in state A’. ' , Let us study this case a little more closely. First of all, we want to suppose that when it is in state A the machine prints ‘1 am in state A’ without first passing through any other states. That is, in every row of the column of the table headed ‘state A’ there appears the instruction: print‘r ‘I am in state A’. Secondly, by way of comparison, let us consider a human being, Jones, who says ‘I am in pain’ (or ‘Ouchl’, or ‘Something hurts’) whenever he is in pain. To make the .comparison as close as possible, we will have to suppose that Jones’ linguistic conditioning is such that he? simply says ‘I am in pain’ ‘without thinking ’, i.e. without passing through any introspectible mental states other than the pain itself. In Wittgenstein’s terminology, Jones simply evince: his pain by saying ‘I am in pain’ — he does not first reflect on it (or heed it, or note it, etc.) and then consciously describe it. (Note that this simple possibility of uttering the ‘proposition’, ‘1 am in pain’ without first performing any mental ‘act of judgement’ was overlooked by traditional epistemologists from Hume to Russell!) Now we may consider the parallel question ‘Does the machine “ascertain” Lhat it is in state A?’ and ‘Does Jones “know” that he is in pain?’ and their consequences. Philosophers interested in semantical questions have, as one might expect, paid a good deal of attention to the verb ‘know’. Traditionally, three elements have been distinguished: (i) ‘X know that p’ implies that p is true (we may call this the truth element); (2) ‘X knows that 13’ implies that X believes that p (philosophers have quarrelled about the word, some contending that it should be ‘X is confident that p,’ or ‘X is in a position to assert that p’; I shall call this element the confidence element); (3) ‘X knows that p’ implies that X has evidence that 1) (here I think the word ‘evidence’ is definitely wrong,I but it will not matter for present purposes; I shall call this the evidential element). Moreover, T Here it is necessary to suppose that the entire sentence ‘ I am in state A. ’ counts as a single symbol in the machine’s alphabet. I For example, I know that the sun is 93 million miles from the earth, but I have no evidence that this is so. In fact, I do not even remember where I learned this. 368 it is part of the meaning of literally evidence for itself: be different things. In View of such anal ‘ theword ‘evidence’ that nothing can be if X is ev1dence for Y, then X and Y must follows: it would be cl pain; but either Jones a pain. Against these Jones is in a position to nfidence elements are both present; it is the evidential element that occasions the difficulty ) I . . . rath do nolt1 WlSh to argue this question here ;'l‘ the present concern is er Wit the Similarities between our two questions For example I g $ ’ 0116 1111 ht declde to accept (as 11011 deHaIlt lOglcally In OI dCI 11011 SCHCOIIU adlCtOI y , etc.) tile tWO Statelllellts. (a) The machine ascertained that it was in state A (b) Jones knew that he had a pain, , or one might reject both. If one rejects alternative formulations which are certain (for (a)) ‘The machine was in state A an in state A’”, (for (b)) ‘Jones was in ‘ - ' u 1 ' am in pain (or, ‘Jones was in pai am in pain” ’). On the ’ questions pthe‘rfljand, if one accepts (a) and (b), then one must face the al) 020 did the machine ascertain that it was in state A” and (b1) ‘How did Jones know that he had a And if one regards these que ' (a) and (b), then one can find ly semantically acceptable: e.g. . (1 this caused it to print: “I am pain, and this caused him to say “I n, and he evinced this by saying “I want to find that this sentence is deviant. 369 MIND, LANGUAGE AND REALITY will be degenerate answers — e.g. ‘By being in state A ’ and ‘By having the pain.’ At this point it is, I believe, very clear that the difficulty has in both cases the same cause. Namely, the difficulty is occasioned by the fact that the ‘ve...
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