Alan Turing: The Enigma The Centenary Edition

by Andrew Hodges

  ECRASIA: Cannot he do anything original?

  PYGMALION: No. But then, you know, I do not admit that any of us can do anything really original, though Martellus thinks we can.

  ACIS: Can he answer a question?

  PYGMALION: Oh yes. A question is a stimulus, you know. Ask him one.

  Much of what Alan wrote was a justification of Pygmalion’s argument, which Shaw, champion of the Life Force, had derided.

  This time he also offered a very carefully phrased prophecy, made deliberately rather than off the cuff to newspaper reporters.

  I believe that in about fifty years’ time it will be possible to programme computers, with a storage capacity of about 109, to make them play the imitation game so well that an average interrogator will not have more than 70 per cent chance of making the right identification after five minutes of questioning. The original question, ‘Can machines think?’ I 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.

  These conditions (‘average’, ‘five minutes’, ‘70 per cent’) were not very demanding. But it was most important that the ‘imitation game’ would allow questions about anything whatever, not just about mathematics or chess.

  It reflected his all-or-nothing intellectual daring, and it came at an appropriate moment. A first generation of pioneers in the new sciences of information and communication, people like von Neumann, Wiener, Shannon, and pre-eminently Alan Turing himself, who had combined broad insights into science and philosophy with the experience of the Second World War, was giving way to a second generation which possessed the administrative and technical skills to build the actual machines. The broad insight, and the short-term skill, had little in common – that was one of Alan’s problems. This paper was something of a swan song for the primal urge, bequeathing the original excitement to the world before it was submerged in mundane technicalities. As such it was a classic work in the British philosophical tradition. It was a gentle reproof to the ponderous essays by Norbert Wiener, as well as to the reactionary, ‘soupy’ trend of English culture in the late 1940s. Bertrand Russell admired it, and his friend Rupert Crawshay-Williams wrote appreciatively to Alan of how much Russell and he had enjoyed reading it.35

  From a philosophical point of view, it could be said to fit in with Gilbert Ryle’s The Concept of Mind, which had appeared in 1949, and which put forward the idea of mind not as something added to the brain, but as a kind of description of the world. But Alan’s paper proposed a specific kind of description, namely that of the discrete state machine. And he was more the scientist than the philosopher. The point of his approach, as he stressed in the paper, was not to talk about it in the abstract, but to try it out and see how much could be achieved. In this he was the Galileo of a new science. Galileo made a practical start upon that abstract model of the world called physics; Alan Turing upon that model provided by the logical machine.

  Alan himself would have liked the comparison: he made reference in the article to Galileo incurring the displeasure of the church and the format of his ‘Objections’ and ‘Refutations’ was one of a trial. A year or so later he gave a talk36 on this subject subtitled ‘A Heretical Theory’. He liked to say things like: ‘One day ladies will take their computers for walks in the park and tell each other “My little computer said such a funny thing this morning!”,’ to destroy any sort of sanctimonious forelock-touching to the ‘higher realms’. Or, when asked how to make a computer say something surprising, he answered ‘Get a bishop to talk to it.’ In 1950 he was hardly likely to be on trial for heresy. But he certainly felt himself up against an irrational, superstitious barrier, and his predisposition was to defy it. He continued:

  I believe further that no useful purpose is served by concealing these beliefs. The popular view that scientists proceed inexorably from well-established fact to well-established fact, never being influenced by any unproved conjecture, is quite mistaken. Provided it is made clear which are proved facts and which are conjectures, no harm can result. Conjectures are of great importance since they suggest useful lines of research.

  Science, to Alan Turing, was thinking for himself.

  Untarnished by all the trials and errors surrounding the actual computer installations, sprang out this ‘conjecture’: the achievement by the millennium of something approaching the artificial intelligence that had long been expressed in the myth of Pygmalion. Also emerging fully-formed was the fruit of his thought since 1935 on the discrete state machine model, on universality, and the constructive use of the imitation principle to ‘build a brain’.

  Nonetheless, beneath the assertive surface of the paper lay probing, needling, teasing questions. For this was not tunnel vision. Unlike so many scientists, Alan Turing was not trapped within the narrow framework within which his ideas were formed. Polanyi was keen on pointing out the different models employed by the different branches of scientific enquiry, and the importance of distinguishing them. But Edward Carpenter had gone to the heart of the matter long before:37

  The method of Science is the method of all mundane knowledge; it is that of limitation or actual ignorance. Placed in face of the great uncontained unity of Nature we can only deal with it in thought by selecting certain details and isolating those (either wilfully or unconsciously) from the rest.

  To model the activity of the brain as a ‘discrete controlling machine’ was a good example of ‘selecting certain details’, since the brain could, if desired, be described in many other ways. Alan’s thesis was, however, that this was the model relevant to what was called ‘thinking’. As he said a little later,38 in a parody of Jefferson’s argument, ‘We are not interested in the fact that the brain has the consistency of cold porridge. We don’t want to say “This machine’s quite hard, so it isn’t a brain, and so it can’t think”.’ Or as he wrote in this paper,

  We do not wish to penalise the machine for its inability to shine in beauty competitions, nor to penalise a man for losing in a race against an aeroplane. The conditions of our game make these disabilities irrelevant. The ‘witnesses’ can brag, if they consider it advisable, as much as they please about their charms, strength, or heroism, but the interrogator cannot demand practical demonstrations.

  There could be arguments about his thesis within this model, or there could be arguments about the model. The discussion of Gödel’s theorem was, par excellence, one which accepted the model of a logical system. But alive to the philosophy of science, Alan discussed the validity of the model itself. In particular, there was the fact that no physical machine could really be ‘discrete’:

  Strictly speaking there are no such machines. Everything really moves continuously. But there are many kinds of machine which can profitably be thought of as being discrete-state machines. For instance in considering the switches for a lighting system it is a convenient fiction that each switch must be definitely on or definitely off. There must be intermediate positions, but for most purposes we can forget about them.

  That ‘forgetting about them’ would be precisely the element of ‘selecting certain details’ necessary to the scientific method. He conceded that the nervous system was itself continuous, and therefore

  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.

  But he argued that whatever kinds of continuous or random elements were involved in the system – as long as the brain worked in some definite way, in fact – it could be simulated as closely as one pleased by a discrete machine. This was reasonable since it was only applying the same method of approximation as worked very well in most applied
mathematics and in the replacement of analogue by digital devices.

  Natural Wonders had begun by proposing the question, ‘What have I in common with other living things, and how do I differ from them?’ Now Alan was asking what he had in common with a computer, and in what ways he differed. Besides the distinction of ‘continuous’ and ‘discrete’, there was also that of ‘controlling’ and ‘active’ to consider. Here he met the question as to whether his senses, muscular activity and bodily chemistry, were irrelevant to ‘thinking’, or at least, whether they could be absorbed into a purely ‘controlling’ model in which the physical effects did not matter. Discussing this problem, he wrote:

  It will not be possible to apply exactly the same teaching process to the machine as to a normal child. It will not, for instance, be provided with legs, so that it could not be asked to go out and fill the coal scuttle. Possibly it might not have eyes. But however well these deficiencies might be overcome by clever engineering, one could not send the creature to school without the other children making excessive fun of it. It must be given some tuition. We need not be too concerned about the legs, eyes, etc. The example of Miss Helen Keller shows that education can take place provided that communication in both directions between teacher and pupil can take place by some means or other.

  He was not dogmatic about this line of argument. At the end of the article he wrote (perhaps so as to be on the safe side):

  It can also be maintained that it is best to provide the machine with the best sense organs that money can buy, and then teach it to understand and speak English. This process could follow the normal teaching of a child. Things would be pointed out and named, etc. Again I do not know what the right answer is, but I think both approaches should be tried.

  But this was not where he placed his own bets. Later he went as far as to say:39

  … I certainly hope and believe that no great efforts will be put into making machines with the most distinctively human, but non-intellectual characteristics, such as the shape of the human body. It appears to me to be quite futile to make such attempts and their results would have something like the unpleasant quality of artificial flowers. Attempts to produce a thinking machine seem to me to be in a different category.

  In the subjects proposed for automation in 1948, he had been careful to choose those which involved no ‘contact with the outside world’. Chess playing, pre-eminently, would involve no relevant fact but the state of the chessboard and the state of the players’ brains. The same could certainly be claimed of mathematics, and indeed of any purely symbolic system, involving anything technical, any matter of technique. He himself had included cryptanalysis in this scope, but hesitated over language translation. The Mind paper, however, boldly extended the range of ‘intelligent machinery’ to general conversation. As such it was vulnerable to his own criticism, that it would require ‘contact with the outside world’ for this to be possible.

  He did not meet the problem that to speak seriously is to act, and not only to issue a string of symbols. Speech may be uttered in order to effect changes in the world, changes inextricably connected with the meaning of the words uttered. The word ‘meaning’ led Polanyi into extra-material, religious connotations, but there is nothing at all supernatural about the mundane fact that human brains are connected with the world by devices other than a teleprinter. A ‘controlling machine’ was to have physical effects ‘as small as we please’, but speech, to be audible or legible, has to have a definite physical effect, tied into the structure of the outside world. The Turing model held that this was an irrelevant fact, to be discarded in the selecting of certain details, but the argument for this irrelevance was left weakly supported.

  If, as Alan Turing himself suggested, knowledge and intelligence in human beings derive from interaction with the world, then that knowledge must be stored in human brains in some way that depends upon the nature of that interaction. The structure of the brain must connect the words it stores, with the occasions for using those words, and with the fists and tears, blushes and fright associated with them, or for which they substitute. Could the words be stored for ‘intelligent’ use, within a discrete state machine model of the brain, unless that model were also equipped with the brain’s sensory and motor and chemical peripheries? Is there intelligence without life? Is there mind without communication? Is there language without living? Is there thought without experience? These were the questions posed by Alan Turing’s argument – questions close to those that worried Wittgenstein. Is language a game, or must it have a connection with real life? For chess thinking, for mathematical thinking, for technical thinking and any kind of purely symbolic problem-solving, there were arguments of great force behind Alan’s view. But in extending it to the domain of all human communication the questions he raised were not properly faced, let alone resolved.

  Indeed, they had been faced more openly in the 1948 report, in choosing activities for a ‘disembodied’ brain. He had narrowed them down to those not requiring ‘senses or locomotion’. But even there, in his choice of cryptanalysis as a suitable field for intelligent machinery, he had played down the difficulties arising from human interaction. To portray cryptanalysis as a purely symbolic activity was very much a Hut 8 view of the war, sheltered from the politics and military activity, and trying to work in a self-contained way without interference from outside. The hero of The Small Back Room had said rather ironically:

  It’s a great pity when you come to think of it that we can’t abolish the Navy, the Army and the Air Force and just get on with winning the war without them.

  But they could not do without the fighting services. There had to be some integration of Intelligence and Operations, in order for Bletchley to have any meaning. Indeed, the difficulty of the authorities was that of trying to draw a line between them, where no line really existed. The intelligence analysts invaded the field of appreciation. Appreciation held consequences for operations, which in turn were necessary for more effective cryptanalysis. But the Operations actually happened, in the war-winning, ship-sinking physical world. It was hard to believe in Hut 8, where the war was like a dream, but they were actually doing something.

  To the mathematicians, it might well be tempting to regard the machines and the pieces of paper as purely symbolic. But the fact that they had physical embodiment mattered very much to those for whom knowledge was power. If there was a real secret to Bletchley it lay in the integration of those different kinds of description of its activities: logical, political, economic, social. It was so complex, not just within one system, but in its meshing of many systems, that a Churchillian ‘Spirit of Britain’ was as good an explanation of how it worked as any. But Alan had always leant towards keeping his work self-contained, as a technical puzzle, and was resistant to what he regarded as administrative interference. It was the same problem with his model of the brain, as in his work for the Brain of Britain. There was the same problem again, in the fate of the ACE. Having set down a highly intelligent plan, Alan tended to assume that the political wheels would turn as if by magic to put it into effect. He never allowed for the interaction required to achieve anything in the real world.

  This was the objection that lay at the heart of Jefferson’s remarks, confused as they might be. It was not that Alan avoided it entirely, for he went as far as to concede:

  There are, however, special remarks to be made about many of the disabilities that have been mentioned. The inability to enjoy strawberries and cream may have struck the reader as frivolous. Possibly a machine might be made to enjoy this delicious dish, but any attempt to make one do so would be idiotic. What is important about this disability is that it contributes to some of the other disabilities, e.g. to the difficulty of the same kind of friendliness occurring between man and machine as between white man and white man, or black man and black man.

  Yet this was not a special, but a very substantial concession, opening up the whole question as to the part played by such human faculties,
in the ‘intelligent’ use of language. This question he failed to explore.

  In a rather similar way, he did not avoid giving a direct answer to Jefferson’s objection that a machine could not appreciate a sonnet ‘because of emotions genuinely felt’. Jefferson’s ‘sonnets’ had about them the quality of Churchill’s advice to R.V. Jones:40 ‘Praise the humanities, my boy. That’ll make them think you’re broadminded!’ – and accordingly, Alan fastened on to the phoney culture of this Shakespeare-brandishing, perhaps a little cruelly. He rested his case on the imitation principle. If a machine could argue as apparently genuinely as a human being, then how could it be denied the existence of feelings that would normally be credited to a human respondent? He gave a paradigm conversation to illustrate what he had in mind:

  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 that Mr Pickwick reminded you of Christmas?