Re: Turing: Computing Machinery and Intelligence

From: Marinho Francis-Oladipo (
Date: Tue Mar 27 2001 - 18:49:08 BST

Turing, A. M. (1950) Computing Machinery and Intelligence.
Mind 49:433-460.

This paper is Alan Turing's attempt at trying to solve the question of
whether computers are able to think for themselves. If it could be proved
that this was possible, then it would probably have been easy to deduce
therefore that they were also intelligent. At the time, and until now, the
true essence of what is captured by intelligence is still unidentifiable.
It is easier to compare the relative intelligence of two or more
individuals than it is to specify what is intelligent and why it is or can
be labelled intelligent. In order to commence his quest for the answer to
the proposed question, Mr Turing first shows that the question in itself
was much too ambiguous and as a result, probably wouldn't have a chance to
be answered fairly.

>If the meaning of the words "machine" and "think" are to be found by
>examining how they are commonly used it is difficult to escape the
>conclusion that the meaning and the answer to the question, "Can machines
>think?" is to be sought in a statistical survey such as a Gallup poll.

Once it has been established that the question is inappropriate, Alan
Turing proceeds to restructure the question into a form that he feels is
more defined and as a result easier to answer. Turing's revised question
is described in the form of a game played by three human participants.

>The new form of the problem can be described in terms of a game which we
>call the 'imitation game." 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 front 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

To avoid the problem of physical, vocal and other obvious differences
between the sexes, the candidates communication with the interrogator
is typewritten. Turing's game requires the male candidate to misguide the
interrogator's identification while the female candidate's job is to aid
the interrogator by telling the truth. This is where the question of the
thinking computer comes in because Turing then considers what will happen
if a computer replaced the candidate A in the game.

>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?

Turing has described this as a game, and that implies that the object is
to win or avoid losing. The interrogator wins if the man and woman
candidates can be correctly identified after interrogation otherwise,
they lose. Turing's description of the game could leave readers of the
opinion that the objective is to try and fool someone. Moreover, Turing
refers to the frequency of correct or wrong identifications. Does the
frequency of correct identifications actually specify intelligence?
The original question is to find out if computers are intelligent, not to
find out how much more or less intelligent they are than man.

So a computer replaces the male candidate mid-game, Turing's replacement
question is how much more often the interrogator will make incorrect
classifications. I don't think that this is the question that Turing meant
to ask. Is it relevant? What if the male candidate was replaced by
another male candidate instead of a computer? The interrogator will
surely not arrive at the same number of correct and wrong identifications
in both cases. What does this mean? Does it mean that one man is
intelligent and the other isn't? Or is one more intelligent than the
other? The question that maybe should have been asked instead is whether
the interrogator would notice that there had been a substitution.

Alan Turing then goes on to expansiate on the precise definition of
machines and in so doing, excludes all non-digital computers from the

>Following this suggestion we only permit digital computers to take part
>in our game.

I do not disagree with him on this viewpoint but I'm not sure i understand
his manner of reasoning for the exclusion. He declares that a human being
created entirely from a single cell would probably not be categorised as a
thinking machine and i am inclined to agree because even though the new
human has not been born in the usual manner, he or she more than likely
will be as human as one can be. I however do not understand what that has
to do with insisting that all the engineers be of the same sex.

>It is difficult to frame the definitions so as to satisfy these three
>conditions. One might for instance insist that the team of engineers
>should be all of one sex, but this would not really be satisfactory, for
>it is probably possible to rear a complete individual from a single cell
>of the skin (say) of a man.

Turing, having allowed only digital computers to be included in this
experiment, then goes on to expansiate and define a digital computer. His
definition makes a comparison to a human computer.

>The idea behind digital computers may be explained by saying that these
>machines are intended to carry out any operations which could be done by a
>human computer. The human computer is supposed to be following fixed
>rules; he has no authority to deviate from them in any detail.

According to Mr Menabrea's paper on the Analytical Engine, Charles Babbage
identified two distinct sides to the solution of a problem when performed
by humans: a mathematical and an intellectual one. It was the mathematical
aspect that Mr Babbage tried to capture in the description of his machine.
Turing rightly identifies that such a definition of the digital computer as
intending to carry out any operation could be potentially hazardous. But he
claims maybe a bit hastily that the digital computer mimics the actions of
a human computer very closely. It is probably more appropriate to say that
they perform specifically calculations very similarly to the human

>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 above statement alone is enough to see why there has been so much room
for argument on Turing's theory. He uses words like 'play' and 'imitation
game'. This is saying that in his future, he saw a computer being developed
that could deceive an interrogator a proportion of the time that it was
tested. If a machine can think, it can think. We never say an intelligent
person is intelligent half the time so why does Turing try to quantify the
thinking of a machine? Why does he specify that the game is to be played
with an average interrogator? If the interrogator is being fooled so many
times in the test period, is it testing his intelligence as well and
does his intelligence drop the less correct his identifications? Why did
Turing specify a time limit on the game. Surely this is not an endurance
game. The aim is to find out if machines can think not to see how long they
can think for.

Turing next attempts to consider and defend himself against all possible
opinions that oppose his. In doing so, he commences with the theological
objection that suggests that God has only bestowed the ability to think
through an immortal soul on human beings. This leads to the conclusion
that animals and machines cannot think.

> It appears to me that the argument quoted above implies a serious
>restriction of the omnipotence of the Almighty. It is admitted that there
>are certain things that He cannot do such as making one equal to two, but
>should we not believe that He has freedom to confer a soul on an elephant
>if He sees fit?

Turing has a point. Given that God is as powerful as he is meant to be,
surely he can give a soul to anything he deems fit and it is impossible
to know who has a soul and who doesn't as displayed by the other mind's
problem. It is just as impossible to know that another person has a soul.
The only reasoning to suggest this is because we are all similar and of the
same species. Still siding with Turing against the theologists, if God
only gave humans an immortal soul, how can animals sense danger, be taught
things by learning what their owners expect of them? If the bible is taken
as the Gospel truth, why did Noah have to save the animals as well as his
family during the flood?
Taking the theological point of view for a minute, it does say that human
beings were created in God's own image and likeness and no such reference
to any other creature was made so it can probably be assumed therefore that
we are the only ones with souls.

>There are a number of results of mathematical logic which can be used to
>show that there are limitations to the powers of discrete-state machines.
>The short answer to this argument is that although it is established that
>there are limitations to the Powers If any particular machine, it has only
>been stated, without any sort of proof, that no such limitations apply to
>the human intellect.

Once again Turing's point is valid. It is true that there are these bits
of logic that highlight limitations to computation, but it is also true
that the human intellect has not been able to show that it is not
susceptible to the same limitations. As Turing says, there are many
questions that human beings get asked that they cannot answer or get wrong.
The type of questions that these machines are supposed to fail on are
for instance those that require decisive answers about topics that have
no definitive answer.
By the same token, if a human was asked if a similar human would ever
answer 'Yes' to any question, there would definitely be a long pondering
time. Back to the other mind's problem, the individual being asked the
question is not the individual in the question even though they are similar
and so it is not really possible to know how the latter would answer the
question in order for the former to answer correctly. Confused? That's what
i thought. This is the limitation being questioned and it can be seen that
it affects the human as well as the machine.

Turing's next defence is against the argument from those who believe in a

>This argument is very, well expressed in Professor Jefferson's Lister
>Oration for 1949, from which I quote. "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

Here as before, one can only prove that the machine knows it has written
the sonnet by actually becoming the machine in order to get round the
other mind's problem. Searle overcame this barrier in his chinese room
argument which is the pen pal's version of the Turing test. He became the
machine communicating in chinese with the interrogator by implementing
algorithms alone. He showed by so doing that he could communicate endlessly
in chinese without actually understanding a word of the language. This goes
a long way to show that even if a machine can write a sonnet, it can do it
without necessarily knowing what it had done. This suggests that the
consciousness people have a point.

Turing's next opposition is from the various things that are suggested that
computers cannot do that humans can.

>These arguments take the form, "I grant you that you can make machines do
>all the things you have mentioned but you will never be able to make one
>to do X." Numerous features X are suggested in this connexion I offer a

>Be kind, resourceful, beautiful, friendly, have initiative, have a sense
>of humour, tell right from wrong, make mistakes, fall in love, enjoy
>strawberries and cream, make some one 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.

All of these deformities, are similar to the argument concerning emotion,
consciousness. Turing identifies this and provides some argument in his
favour to combat these. For my own addition to his cause, What does beauty
have to do with intellect? There are lots of examples in the world of
beautiful people who are not reknown for their intelligence and by the same
token, there are intelligent people who would not be categorized as
beautiful. By the way, what happened to beauty being in the eyes of the
On the matter of learning from experience, there are lots of machines that
have self modifying code. There are neural networks that show learning by
following some training rule. An example is the learning of simple logic
functions by the single layer percptron using the perceptron training rule.
Turing agrees when he refers to the machine being the subject of its own

>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.

With regards to doing something new, everytime a computer does something
for the first time, it is doing something new. Also with new software
being implemented on it, surely it is doing something new. If the argument
is that humans do not require new software to do something new, then what
is it when they are taught things? Surely it is in effect new data or
rules being presented to them. Lady lovelace's objection is similar to this
and is also defended against by Turing. It has already been decided that
computers can learn from experiences, surely if this is the case, the next
time a similar event is experienced the outcomes of the old experience can
be applied to arrive at a new outcome. In the case of the neural network,
the net starts off unknowledgeable and at the end of its training, it has
learnt how to perform the AND function and can be tested to prove it.

>It is true that a discrete-state machine must be different from a
>continuous machine. But if we adhere to the conditions of the imitation
>game, the interrogator will not be able to take any advantage of this

>It would not be possible for a digital computer to predict exactly what
>answers the differential analyser would give to a problem, but it would be
>quite capable of giving the right sort of answer. For instance, if asked
>to give the value of (actually about 3.1416) it would be reasonable to
>choose at random between the values 3.12, 3.13, 3.14, 3.15, 3.16 with the
>probabilities of 0.05, 0.15, 0.55, 0.19, 0.06 (say). Under these
>circumstances it would be very difficult for the interrogator to
>distinguish the differential analyser from the digital computer.

The entire basis for the imitation game is that it is carried out with a
digital or discrete-state machine. It is quite unsurprising therefore that
the next argument to be contended is one that highlights that the computer
being modelled (the human computer) is not a discrete-state machine. As
Turing states, this fact is irrelevant if the game is played as he
described. He further shows that even though the a continuous machine
cannot be mimicked by a digital computer, they can still both yield the
same sort of answer and therefore there is no point trying to differentiate
between the two.

>A more specific argument based on ESP might run as follows: "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 gets 104 right,
>so the interrogator makes the right identification." There is an
>interesting possibility which opens here. Suppose the digital computer
>contains a random number generator.

>On the other hand, he might be able to guess right without any
>questioning, by clairvoyance. With ESP anything may happen.

Turing suggests that the computer's random number generator will be subject
to the psychokinetic powers of the interrogator. Does the computer need
to have a random number generator? If it just makes a random guess and is
perceptive to the psychokinetic powers, surely it could still make more
correct guesses. In considering the flip side, is Turing referring to the
interrogator or the male candidate making a correct guess? If it turns out
that computers are susceptible to Extrasensory Perception, then in
agreement with Turing, it is necessary to modify the setup for the
imitation game.

Finally, Turing concludes his paper by concerning himself with the topic of
learning machines. He is trying to produce his own arguments to support his
theories after going so far as to pick out the holes in his opposition. He
starts this by focusing on Lady Lovelace's objection.

>Another simile would be an atomic pile of less than critical size: an
>injected idea is to correspond to a neutron entering the pile from
>without. Each such neutron will cause a certain disturbance which
>eventually dies away. If, however, the size of the pile is sufficiently
>increased, tire disturbance caused by such an incoming neutron will very
>likely go on and on increasing until the whole pile is destroyed. Is there
>a corresponding phenomenon for minds, and is there one for machines?

I agree that given an atomic pile, a neutrons interferance would cause the
described disturbance until it dies down. How does Turing then go on to say
that if the pile was large enough, such a disturbance would get greater? Is
that possible? Take for example a pebble dropped into a puddle, the effects
are obvious until as expected the ripples die down. If that same pebble was
dropped in the ocean, it doesn't have this huge impact that Turing's
statement seems to be conveying. If anything, i would say that the effects
will decrease quicker due to the considerable increase in the number of
atoms to provide damping. This analogy therefore does not seem to me to
support Turing's following argument with reference to the subcritical and
supercritical mind.

>Adhering to this analogy we ask, "Can a machine be made to be

Going along with his sub/super critical mind theory, it is obviously an
appropriate question to ask whether machines can be made to be subcritical,
but surely it would be better to see if they can be subcritical first. I
accept that if they can be made to be supercritical then the question
of subcriticality becomes irrelevant but by the same token, if they cannot
be made to be subcritical first, then how are they going to be made

>Our problem then is to find out how to programme these machines to play
>the game.

Once again, Turing has used his description of the test as a game. I think
that Turing had the right idea in many ways but if controversy and
misinterpretation have arisen in the minds of the population as a result of
his paper, then it is mainly down to the manner in which Turing set about
explaining things.
Turing's final thoughts were to entertain the idea that following the human
development, we start as children and through learning from experiences, we
develop into adults. The child mind is assumed with reason to be slightly
less complicated than the adult one. Intelligence, whatever that is, can
nevertheless be seen in children as they adapt and reform ideas through
their experiences until they evolve into their adult forms where they carry
on the learning process. Taking this notion into consideration, Turing's
idea is that instead of trying to model adult intelligence, we model the
child brain and its processes and then, given experiences and guidance, it
might one day become the adult brain that would be considered artificially
Francis Oladipo Marinho

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