Gödel, Escher, Bach: An Eternal Golden Braid (107 page)

"Computing

Machinery

and

Intelligence" and appeared in the journal

Mind
.' I will say some things about that

article, but I would like to precede them

with some remarks about Turing the

man.

Alan Mathison Turing was born in

London in 1912. He was a child full of

curiosity

and

humor.

Gifted

in

mathematics, he went to Cambridge

where his interests in machinery and

mathematical logic cross-fertilized and

resulted in his famous paper on

"computable numbers", in which he

invented the theory of Turing machines

and demonstrated the unsolvability of

the halting problem; it was published in

1937. In the 1940's, his interests turned

from the theory of computing machines

to the actual building of real computers.

He was a major figure in the

development of computers in Britain,

and a staunch defender of Artificial In-

FIGURE 113.
Alan Turing, after a

successful race (May, 1950). [From

Sara

Turing,

Alan

M.

Turing

(Cambridge, U. K.:W. Heffer & Sons,

1959).

telligence when it first came under attack. One of his best friends was David Champernowne (who later worked on computer composition of music). Champernowne and Turing were both avid chess players and invented "round-the-house" chess: after your move, run around the house-if you get back before your opponent has moved, you're entitled to another move. More seriously, Turing and Champernowne invented the first chess playing program, called "Turochamp . Turing died young, at 41-apparently of an accident with chemicals. Or some say suicide. His mother, Sara Turing, wrote his biography. From the people she quotes, one gets the sense that Turing was highly unconventional, even gauche in some ways, but so honest and decent that he was vulnerable to the world. He loved games, chess, children, and bike riding; he was a strong long-distance runner. As a student at Cambridge, he bought himself a second-hand violin and taught himself to play. Though not very musical, he derived a great deal of enjoyment from it. He was somewhat eccentric, given to great bursts of energy in the oddest directions. One area he explored was the problem of morphogenesis in biology.

According to his mother, Turing "had a particular fondness for the
Pickwick Papers
", but

"poetry, with the exception of Shakespeare's, meant nothing to him." Alan Turing was one of the true pioneers in the field of computer science.

The Turing Test

Turing's article begins with the sentence: "I propose to consider the question `Can machines think?"' Since, as he points out, these are loaded terms, it is obvious that we should search for an operational way to approach the question. This, he suggests, is contained in what he calls the "imitation game"; it is nowadays known as the
Turing test
.

Turing introduces it as follows:

It is played with three people: a man (A), a woman (B), and an interrogator (C) who may be of either sex. The interrogator stays in a room apart from the other two. The object of the game for the interrogator is to determine which of the other two is the man and which is the woman. He knows them by labels X and Y, and at the end of the game he says either "X is A and Y is B" or "X is B and Y is A". The interrogator is allowed to put questions to A and B thus:

C: Will X please tell me the length of his or her hair?

Now suppose X is actually A, then A must answer. It is A's object in the game to try to cause C to make the wrong identification. His answer might therefore be

"My hair is shingled, and the longest strands are about nine inches long."

In order that tones of voice may not help the interrogator the answers should be written, or better still, typewritten. The ideal arrangement is to have a teleprinter communicating between the two rooms. Alternatively the questions and answers can be repeated by an intermediary. The object of the game for the third player (B) is to help the interrogator. The best strategy for her is probably to give truthful answers. She can add such things as "I am the woman, don't listen to him!" to her answers, but it will avail nothing as the man can make similar remarks.

We now ask the question, "What will happen when a machine takes the part of A in this game Will the interrogator decide wrongly as often when the game is played like this as he does when the game is played between a man and a woman?

These questions replace our original, "Can machines think?"2

After having spelled out the nature of his test, Turing goes on to make some commentaries on it, which, given the year he was writing in, are quite sophisticated. To begin with, he gives a short hypothetical dialogue between interrogator and interrogatee:3

Q. Please write me a sonnet on the subject of the Forth Bridge [a bridge over the Firth of Forth, in Scotland].

A. Count me out on this one. I never could write poetry.

Q. Add 34957 to 70764.

A. (Pause about 30 seconds and then give as answer) 105621.

Q. Do you play chess?

A. Yes.

Q. I have K at my K1, and no other pieces. You have only K at K6 and R at R1. It is your move. What do you play?

A. (After a pause of 15 seconds) R-R8 mate.

Few readers notice that in the arithmetic problem, not only is there an inordinately long delay, but moreover, the answer given is wrong! This would be easy to account for if the respondent were a human: a mere calculational error. But if the respondent were a machine, a variety of explanations are possible. Here are some:

(1) a run-time error on the hardware level (i.e., an irreproducible fluke); (2) an unintentional hardware (or programming) (reproducibly) causes arithmetical mistakes;

(3) a ploy deliberately inserted by the machine's programmer (or builder) to introduce occasional arithmetical mistakes, so as to trick interrogators; (4) an unanticipated epiphenomenon: the program has a hard time thinking abstractly, and simply made "an honest mistake", which it might not make the next time around;

(5) a joke on the part of the machine itself, deliberately teasing its interrogator.

Reflection on what Turing might have meant by this subtle touch opens up just about all the major philosophical issues connected with Artificial Intelligence.

Turing goes on to point out that

The new problem has the advantage of drawing a fairly sharp line between the physical and the intellectual capacities of a man. . . . We do not wish to penalize the machine for its inability to shine in beauty competitions, nor to penalize a man for losing in a race against an airplane.'

One of the pleasures of the article is to see how far Turing traced out each line of thought, usually turning up a seeming contradiction at some stage and, by refining his concepts, resolving it at a deeper level of analysis. Because of this depth of penetration into the issues. the article still shines after nearly thirty years of tremendous progress in computer development and intensive work in Al. In the following short excerpt you can see some of this rich back-and-forth working of ideas: The game may perhaps be criticized on the ground that the odds are weighted too heavily against the machine. If the man were to try to pretend to be the machine he would clearly make a very poor showing. He would be given away at once by slowness and inaccuracy in arithmetic. May not machines carry out something which ought to be described as thinking but which is very different from what a man does: This objection is a very strong one, but at least we can say that if, nevertheless, a machine can be constructed to play the imitation game satisfactorily, we need not be troubled by this objection.

It might be urged that when playing the "imitation game" the best strategy for the machine may possibly be something other than imitation of the behaviour of a man. This may be, but I think it is unlikely that there is any greet effect of this kind. In any case there is ,no intention to investigate here the theory of the game, and it will be assumed that the best strategy is to try to provide answers that would naturally be given by a mans

Once the test has been proposed and discussed, Turing remarks:

The original question "Can machines think 1 believe to be too meaningless to deserve discussion. Nevertheless, I believe that at the end of the century the use of words and general educated opinion will have altered so much that one will be able to speak of machines thinking without expecting to be contradicted.6

Turing Anticipates Objections

Aware of the storm of opposition that would undoubtedly greet this opinion, he then proceeds to pick apart, concisely and with wry humor, a series of objections to the notion that machines could think. Below I list the nine types of objections he counters, using his own descriptions of them .7 Unfortunately there is not space to reproduce the humorous and ingenious responses he formulated. You may enjoy pondering the objections yourself, and figuring out your own responses.

(1) The Theological Objection. Thinking is a function of man's immortal soul. God has given an immortal soul to every man and woman, but not to any other animal or to machines. Hence no animal or machine can think.

(2) The "Heads in the Sand" Objection. The consequences of machines thinking would be too dreadful. Let us hope and believe that they cannot do so.

(3) The Mathematical Objection. [This is essentially the Lucas argument.

(4) The Argument from Consciousness. "Not until a machine can write a sonnet or compose a concerto because of thoughts and emotions felt, and not by the chance fall of symbols, could we agree that machine equals brainy that is, not only write it but know that it had written it. No mechanism

could feel (and not merely artificially signal, an easy contrivance) pleasure at its successes, grief when its valves fuse, be warmed by flattery, be made miserable by its mistakes, be charmed by sex, be angry or depressed when it cannot get what it wants." [A quote from a certain Professor Jefferson.]

Turing is quite concerned that he should answer this serious objection in full detail.

Accordingly, he devotes quite a bit of space to his answer, and in it he offers another short hypothetical dialogue:'

Interrogator: In the first line of your sonnet which reads "Shall I compare thee to a summer's day", would not "a spring day" do as well or better, Witness: It wouldn't scan.

Interrogator: How about ' a winter's day' ? That would scan all right. Witness: Yes, but nobody wants to be compared to a winter's day. Interrogator: Would you say Mr. Pickwick reminded you of Christmas? Witness: In a way.

Interrogator: Yet Christmas is a winter's day, and I do not think Mr. Pickwick would mind the comparison.

Witness: I don't think you're serious. By a winter's day one means a typical winter's day, rather than a special one like Christmas.

After this dialogue, Turing asks, "What would Professor Jefferson say if the sonnet-writing machine was able to answer like this in the
viva voce
?"

Further objections:

(5) Arguments from various Disabilities. These arguments take the form, "I grant you that you can make machines do all the things that you have mentioned but you will never be able to make one to do X." Numerous features X are suggested in this connection. I offer a selection:

Be kind, resourceful, beautiful, friendly, have initiative, have a sense of humor, tell right from wrong, make mistakes, fall in love, enjoy strawberries and cream, make someone fall in love with it, learn from experience, use words properly, be the subject of its own thought, have as much diversity of behaviour as a man, do something really new.

(6) Lady Lovelace's Objection. Our most detailed information of Babbage's Analytical Engine comes from a memoir by Lady Lovelace. In it she states, "The Analytical Engine has no pretensions to originate anything. It can do whatever we know how to order it to perform" (her italics).

(7) Argument from Continuity in the Nervous System. The nervous system is certainly not a discrete state machine. A small error in the information about the size of a nervous impulse impinging on a neuron may make a large difference to the size of the outgoing impulse. It may be argued that, this being so, one cannot expect to be able to mimic the behaviour of the nervous system with a discrete state system.

(8) The Argument from Informality of Behaviour. It seems to run something like this. "If each man had a definite set of rules of conduct by which he regulated his life he would be no better than a machine. But there are no such rules, so men cannot be machines."

(9) The Argument from Extra-Sensory Perception. Let us play the imitation game, using as witnesses a man who is good as a telepathic receiver, and a digital computer. The interrogator can ask such questions as "What suit

does the card in my right hand belong to?" The man by telepathy or clairvoyance gives the right answer 130 times out of 400 cards. The machine can only guess at random, and perhaps get 104 right, so the interrogator makes the right identification.

As you can see, many of the objections overlap and are related to each other. I have attempted in this book to answer most of them in some way or other, usually far less concisely than Turing did.