Alan Turing, 1950

The Imitation Game

• the original question "can machines think" is replaced by the imitation game

• the imitation game is:

  • three people A, B, C (interrogator). A is a human, B is a machine (or vice-versa)

  • C is allowed to ask questions A and B and has to decide which of A and B is the human

• the problem with the "can machines think" question. The definitions of the terms machines and think could be taken to reflect the normal use of the words, which simplifies to answering the original question using a survey.

Critique of the new problem

"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". Why? Perhaps Turing means that we're more interested in publicly accessible behavior rather than the private impression of what "thinking" should feel like.

"It will be assumed that the best strategy is to try to provide answers that would naturally be given by a man".

Digital Computers

digital computer can be regarded as consisting of three parts:

• Store (RAM): stores information

• Executive Unit (CPU): carries out operations on stored values. E.g.:

  • Add number stored in position 6809 to that in 4302 and put the result back into the latter storage position, coded in 6809430217, 17 being the index of the "add" instruction. Turing calls this 10-digit instruction a packet.

  • if/else, while loops (self referential instructions e.g.)

• Control (Programming): makes sure instructions are carried out in the right order

Universality of Digital Computers

Digital computers can mimic any discrete state machine, they are universal machines.

Didn't understand this part or its importance

Contrary Views on the Main Question

• Is the imitation game a good surrogate for the "can machines think?" question? Turing believes the original question is too meaningless to deserve discussion. Why mention it then?

• The theological objection (not much of interest): only god grants a soul and he did not grant it to animals and machines. Resolution: "in attempting to construct such machines we should not be irreverently usurping His power of creating souls, any more than we are in the procreation of children: rather we are, in either case, instruments of His will providing mansions for the souls that He creates."

• "We like to believe that Man is in some subtle way superior to the rest of creation. It is best if he can be shown to be necessarily superior, for then there is no danger of him losing his commanding position" (connected to the theological argument)

• "limitations to the powers of discrete-state machines. The best known of these results is known as Gödel’s [first incompleteness] theorem, and shows that in any sufficiently powerful logical system statements can be formulated which can neither be proved nor disproved within the system, unless possibly the system itself is inconsistent." Result for a digital computer with infinite capacity: "there are certain things that such a machine cannot do. If it is rigged up to give answers to questions as in the imitation game, there will be some questions to which it will either give a wrong answer, or fail to give an answer at all however much time is allowed for a reply [...] The questions that we know the machines must fail on are of this type, “Consider the machine specified as follows. . . . Will this machine ever answer ‘Yes’ to any question? [...] This is the mathematical result: it is argued that it proves a disability of machines to which the human intellect is not subject." Resolution: "it has only been stated, without any sort of proof, that no such limitations apply to the human intellect. But I do not think this view can be dismissed quite so lightly" (note: this is assuming that the machine and human mind are consistent)

• the argument from consciousness. Turing quotes Professor Jefferson "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 brain—that is, not only write it but know that it had written it". Resolution: "This argument appears to be a denial of the validity of our test. According to the most extreme form of this view the only way by which one could be sure that a machine thinks is to be the machine and to feel oneself thinking. One could then describe these feelings to the world, but of course no one would be justified in taking any notice. Likewise according to this view the only way to know that a man thinks is to be that particular man. It is in fact the solipsist point of view. It may be the most logical view to hold but it makes communication of ideas difficult. A is liable to believe ‘A thinks but B does not’ whilst B believes ‘B thinks but A does not’. Instead of arguing continually over this point it is usual to have the polite convention that everyone thinks. [...] I think that most of those who support the argument from consciousness could be persuaded to abandon it rather than be forced into the solipsist position"

• You can make machines do this but you will never be able to make one to do X. "No support is usually offered for these statements. I believe they are mostly founded on the principle of scientific induction."

  • "The claim that a machine cannot be the subject of its own thought can of course only be answered if it can be shown that the machine has some thought with some subject matter. Nevertheless, ‘the subject matter of a machine’s operations’ does seem to mean something, at least to the people who deal with it. If, for instance, the machine was trying to find a solution of the equation x2 − 40x − 11 = 0 one would be tempted to describe this equation as part of the machine’s subject matter at that moment. In this sort of sense a machine undoubtedly can be its own subject matter. It may be used to help in making up its own programmes, or to predict the effect of alterations in its own structure. By observing the results of its own behaviour it can modify its own programmes so as to achieve some purpose more effectively. These are possibilities of the near future, rather than Utopian dreams"

  • a machine can ‘never do anything really new’. This may be parried for a moment with the saw, ‘There is nothing new under the sun’. Who can be certain that 'original work' was not simply [...] the effect of following well-known general principles.