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three substantial claims must be true: first, consciousness is necessary for intelligence; second,
philosophical zombies are possible; and third, the Turing test is a criterion for thinking in all
possible worlds (including those containing zombies). Showing that these claims are all true
is a big ask.
Turing himself replied to Jefferson in a different way: if behaviour is not a sign of conscious-
ness, he said, this must apply to human behaviour as well as to machine behaviour—and the
consequence is that ‘the only way to know that a man thinks is to be that particular man’. This,
he said, is ‘the solipsist point of view’—the claim that (at least, for all I know) I am alone in the
world and everything else is a figment of my mind. Turing assumed that most people, including
Jefferson, would accept the imitation game as a test of thinking rather than be committed to
solipsism. In response, some philosophers have conceded that behaviour is a sign of conscious-
ness, but only in humans, not in machines. This move, though, plays into Turing’s hands. In
1947 he said that ‘fair play must be given to the machine’.^53 In the present context, this puts
the burden of proof on the AI sceptic to show that behaviour is a sign of consciousness only
in humans—without pre-judging the question at issue, namely whether a machine devoid of
consciousness could pass the Turing test. Another big ask.
Heads in the sand
Turing said that many people are ‘extremely opposed’ to the idea of a machine that thinks, and
that this is ‘simply because they do not like the idea’. This explains why much of his writing on
machine intelligence consists of replies to objections. In Turing’s view, the ‘unwillingness to
admit the possibility that mankind can have any rivals in intellectual power’ occurs ‘as much
amongst intellectual people as amongst others: they have more to lose’. This is the ‘heads-in-the-
sand’ objection to thinking machines.^54 (The opposite reaction is panic—fear that machines
will take jobs from, and even lead to the extinction of, humans.^55 ) Is there a whiff of heads-in-
the-sand in the reaction to Deep Blue, Watson, or AlphaGo?
In 1951, in a much-discussed book that attracted a response from Albert Einstein, Viscount
Samuel claimed that the chess player is ‘evidently of a different order from the chess-board and
the pieces’—the chess player possesses ‘[i]ntellectual creativity’, which is ‘not material’. At the
time a critic claimed that, on the contrary, the emergence of chess-playing programs ‘forces
us to admit the possibility of mechanized thinking or to restrict in a very special way our con-
cept of thinking’. Turing himself predicted the last move: he said that, whenever a machine
is deemed to have an ability usually reserved for human beings, people claim that how the
machine does this is ‘really rather base’—they say, ‘Well, yes, I see that a machine could do all
that, but I wouldn’t call it thinking’.^56 This is exactly how, half a century later, critics of Deep Blue
and Watson responded.
But can we react in this way every time? Turing’s famous ‘skin of an onion’ analogy points to
a difficulty:^57
In considering the functions of the mind or the 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 if we are 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 whole
mind is mechanical.