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> ## TL;DR: In this presentation given by A. Turing in 1951 argues...
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This posthumous essay begins an
occasioned
feature in which will appear
documents, usually
translations,
otherwise not readily
available.
Intelligent Machinery, A Heretical Theory*
A. M. TURING
'You cannot make a machine to think for you.' This is a commonplace that
is usually accepted without question. It will be the purpose of this paper
to question it.
Most machinery developed for commercial purposes is intended to carry
out some very specific job, and to carry it out with certainty and consider-
able speed. Very often it does the same series of operations over and over
again without any variety. This fact about the actual machinery available
is a powerful argument to many in favour of the slogan quoted above. To a
mathematical logician this argument is not available, for it has been shown
that there are machines theoretically possible which will do something very
close to thinking. They will, for instance, test the validity of a formal proof
in the system of Principia Mathematica, or even tell of a formula of that
system whether it is provable or disprovable. In the case that the formula is
neither provable nor disprovable such a machine certainly does not behave
in a very satisfactory manner, for it continues to work indefinitely without
producing any result at all, but this cannot be regarded as very different
from the reaction of the mathematicians, who have for instance worked for
hundreds of years on the question as to whether Fermant's last theorem is
true or not. For the case of
machines
of
this
kind a more subtle kind of argu-
ment is necessary. By Godel's famous theorem, or some similar argument,
one can show that however the machine is constructed there are bound to
be cases where the machine fails to give an answer, but a mathematician
would be able to. On the other hand, the machine has certain advantages
over the mathematician. Whatever it does can be relied upon, assuming
no mechanical 'breakdown', whereas the mathematician makes a certain
proportion of mistakes. I believe that this danger of the mathematician
making mistakes is an unavoidable corollary of his power of sometimes hit-
ting upon an entirely new method. This seems to be confirmed by the well
known fact that the most reliable people will not usually hit upon really
new methods.
* © P. N. Furbank, for the Turing estate. Reprinted with permission.
PHILOSOPHIA MATHEMATICA (3) Vol. 4 (1996), pp. 25&-260.
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INTELLIGENT MACHINERY
257
My contention
is
that machines
can be
constructed which will simulate
the behaviour
of the
human mind very closely. They will make mistakes
at
times,
and at
times they
may
make
new and
very interesting statements,
and
on the
whole the output
of
them will
be
worth attention
to
the same sort
of extent
as the
output
of a
human mind.
The
content
of
this statement lies
in
the
greater frequency expected
for the
true statements,
and it
cannot,
I
think,
be
given
an
exact statement.
It
would
not, for
instance,
be
sufficient
to
say
simply that
the
machine will make
any
true statement sooner
or
later,
for an
example
of
such
a
machine would
be one
which makes
all
possible statements sooner
or
later.
We
know
how to
construct these,
and
as they would (probably) produce true
and
false statements about equally
frequently, their verdicts would
be
quite worthless.
It
would
be the
actual
reaction
of the
machine
to
circumstances that would prove
my
contention,
if indeed
it can be
proved
at all.
Let
us go
rather more carefully into
the
nature
of
this
'proof. It is
clearly possible
to
produce
a
machine which would give
a
very good
ac-
count
of
itself
for any
range
of
tests,
if the
machine were made sufficiently
elaborate. However, this again would hardly
be
considered
an
adequate
proof.
Such
a
machine would give itself away
by
making
the
same sort
of
mistake over
and
over again,
and
being quite unable
to
correct
itself, or to
be corrected
by
argument from outside.
If the
machine were able
in
some
way
to
'learn
by
experience'
it
would
be
much more impressive.
If
this were
the case there seems
to be no
real reason
why one
should
not
start from
a comparatively simple machine,
and, by
subjecting
it to a
suitable range
of 'experience' transform
it
into
one
which
was
much more elaborate,
and
was able
to
deal with
a far
greater range
of
contingencies. This process
could propably
be
hastened
by a
suitable selection
of the
experiences
to
which
it
was subjected. This might
be
called 'education'.
But
here we have
to
be
careful.
It
would
be
quite easy
to
arrange
the
experiences
in
such
a
way that they automatically caused
the
structure
of the
machine
to
build
up into
a
previously intended form,
and
this would obviously
be a
gross
form
of
cheating, almost
on a par
with having
a man
inside
the
machine.
Here again
the
criterion
as to
what would
be
considered reasonable
in the
way
of
'education' cannot
be put
into mathematical terms,
but I
suggest
that
the
following would
be
adequate
in
practice.
Let us
suppose that
it is
intended that
the
machine shall understand English,
and
that owing
to its
having
no
hands
or
feet,
and not
needing
to eat, not
desiring
to
smoke,
it
will occupy
its
time mostly
in
playing games such
as
Chess
and GO, and
possibly Bridge.
The
machine
is
provided with
a
typewriter keyboard
on
which
any
remarks
to it are
typed,
and it
also types
out any
remarks that
it wishes
to
make.
I
suggest that
the
education
of the
machine should
be
entrusted
to
some highly competent schoolmaster
who is
interested
in the
project
but who is
forbidden
any
detailed knowledge
of the
inner workings
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258 TURING
of the machine. The mechanic who has constructed the machine, however,
is permitted to keep the machine in running order, and if he suspects that
the machine has been operating incorrectly may put it back to one of its
previous positions and ask the schoolmaster to repeat his lessons from that
point on, but he may not take any part in the teaching. Since this proce-
dure would only serve to test the bona fides of the mechanic, I need hardly
say that it would not be adopted in the experimental stages. As I see it,
this education process would in practice be an essential to the production
of a reasonably intelligent machine within a reasonably short space of time.
The human analogy alone suggests this.
I may now give some indication of the way in which such a machine
might be expected to function. The machine would incorporate a memory.
This does not need very much explanation. It would simply be a list of all
the statements that had been made to it or by it, and all the moves it had
made and the cards it had played in its games. These would be listed in
chronological order. Besides this straightforward memory there would be a
number of 'indexes of experiences'. To explain this idea I will suggest the
form which one such index might possibly take. It might be an alphabetical
index of the words that had been used giving the 'times' at which they had
been used, so that they could be looked up in the memory. Another such
index might contain patterns of men or parts of a GO board that had
occurred. At comparatively late stages of education the memory might be
extended to include important parts of the configuration of the machine
at each moment, or in other words it would begin to remember what its
thoughts had been. This would give rise to fruitful new forms of indexing.
New forms of index might be introduced on account of special features
observed in the indexes already used. The indexes would be used in this sort
of
way.
Whenever a choice has to be made as to what to do next features of
the present situation are looked up in the indexes available, and the previous
choice in the similar situations, and the outcome, good or bad, is discovered.
The new choice is made accordingly. This raises a number of problems. If
some of the indications are favourable and some are unfavourable what
is one to do? The answer to this will probably differ from machine to
machine and will also vary with its degree of education. At first probably
some quite crude rule will suffice, e.g., to do whichever has the greatest
number of votes in its favour. At a very late stage of education the whole
question of procedure in such cases will probably have been investigated by
the machine
itself,
by means of some kind of index, and this may result in
some highly sophisticated, and, one hopes, highly satisfactory, form of rule.
It seems probable however that the comparatively crude forms of rule will
themselves be reasonably satisfactory, so that progress can on the whole
be made in spite of the crudeness of the choice rules. This seems to be
verified by the fact that Engineering problems are sometimes solved by the
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