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Philosophy 4610
Philosophy of Mind
Week 8: Can a Computer Think?
Turing and Computers
 Alan Turing (1912-1954)
 During World War II, Turing’s
work on code-breaking was
instrumental in breaking the
“Enigma” code used by the
German and Japanese
 Because of this work, Turing
has been called the single
figure most responsible for
the Allied victory in the war.
Turing and the Enigma
 The enigma machine used a
series of rotors to encode any
message in a way that
depended on the particular
settings for that day
 Turing’s task was to find a way
to decode a coded message
using only guesses about some
of the words likely to appear in
 To solve the problem, Turing’s
team developed a massively
complicated machine called
the “Bombe” that eventually
succeeded in breaking the
enigma code
 Although this machine was
very complicated, it was not a
computer in the modern sense
because it had only one, fixed
Turing’s Prediction (1950)
 “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 …”
Computer thinking and Artificial
 Turing’s prediction from 1950 inaugurated
the field of artificial intelligence. In this field,
researchers are trying to build a computer or
artificial system that could actually think or
be intelligent.
 How might we define “thinking”?
 Does Turing’s prediction hold true? If it
does not already, when will it hold true?
Artificial Intelligence:
What are the Bounds?
 Since 1950, tasks once
thought possible only
for human beings have
again and again been
accomplished by
 Are there limits to this
progress? Is there
anything that humans
can do that computers
or machines never will
be able to?
Turing: The “Turing Test”
 Turing considers the question: “Can
Computers Think?”
 But this question is unclear and difficult to
answer. Turing suggests replacing it with
another question, which he puts in the form
of an “imitation game” or “test”
The Turing Test
 A judge is connected to
two subjects by teletype
 One of the subjects is a
machine and the other is
a person: the judge
doesn’t know which is
 If the machine can fool
the judge into believing it
is a person, it is actually
The Turing Test
 “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.” (p. 4)
 Do we agree with Turing? If a computer can pass
the Turing test 70% of the time, is it actually
The Turing Test:
Questions and Objections
 Is there anything essential that a human
being can do that a computer could never
do? Why?
 Even if a computer can pass a Turing test,
how do we know it is really thinking as
opposed to imitating or simulating thought?
 If the Turing test is not a good test for actual
thinking, is there any better test?
Computer Thinking:
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.” (p. 5)
1) If God can create bodies and attach souls to them,
he could also attach souls to computers
2) Theological arguments are unsatisfactory for
establishing scientific conclusions
Computer Thinking:
2) The “Heads in the Sand” Objection:
“The consequences of machines thinking would be
too dreadful. Let’s hope and believe that they
cannot do so.” (p. 6)
Response: This is not really an argument at all,
but just an appeal for consolation.
Computer Thinking:
4) The Argument from Consciousness:
“No machine could feel (and not merely artificially signal ...)
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.” (Geoffery Jefferson, 1949 (P. 6))
Response: If it is impossible to know that a machine is
really conscious judging from its responses, then it is
impossible to know whether any other person is really
conscious as well. If the Turing test could not show that a
computer is really thinking, then it is impossible for me to
show that anyone else (other than myself) is really thinking.
Computer Thinking:
5) Arguments from Various Disabilities:
No computer could ever do X (where X is, e.g. “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.” (p. 8)
Response: Various, but all of these seem to be based on
a bad extrapolation from what we have seen before. Some
of the computers we have seen cannot do these things, but
that is no reason to think we could not eventually build a
computer that can.
Computer Thinking:
6) Lady Lovelace’s Objection:
Computers only do what they are programmed to do,
so it is impossible for a computer ever to learn
something new or do something unexpected
Response: Computers do “new” and surprising
things all the time. It is also easily possible for us
to set up a mechanism whereby a computer can
modify its own program, and thereby can be said
to have “learned.”
Computer Thinking:
Minds and Machines
 “The ‘skin-of-an-onion analogy is also helpful. In
considering the functions of the mind or brain we
find certain operations which we can explain in
purely mechanical terms. This we say does not
correspond to the real mind: it is a sort of skin
which we must strip off to find the real mind. But
then in what remains we find a further skin to be
stripped off, and so on. Proceeding in this way do
we ever come to the ‘real’ mind, or do we
eventually come to the skin which has nothing in
it? In the latter case the mind is mechanical.”
(Turing, p. 12)
Computer Thinking:
 Turing suggested that computers could think and
he suggested the Turing test to determine whether
they can think.
 If we accept the test, it will be difficult to hold onto
a dualist or theological view of human
 On the other hand, it is not obvious how to explain
consciousness or the possibility of a physical
organism giving rise to experience at all