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Philosophy and Cogsci
The Turing Test
Joe Lau
Alan Turing (1912-1954)
 Famous
British mathematician /
logician

Mathematical theory of
computation.
 Helped
cracked the German Uboat Enigma code in WWII.
 A homosexual, arrested in 1952.
 Committed suicide.
More information
 More

on Turing’s life :
Turing’s biographer Andrew Hodges :
http://www.turing.com/turing/Turing.html
 Computation


theory
Book : Boolos and Jeffrey’s
Computability and Logic
Article : in Stanford Encyclopaedia of
Philosophy (web)
Topic
paper in Mind “Computing
Machinery and Intelligence”
 1950
Introduced computers to
philosophy
 Argued for the plausibility of
thinking machines
 Proposed “Turing test” often cited
as criterion of success for AI.

Turing’s Proposal
 The
question “Can machines
think?” is too vague.
What are machines?
 What is thinking?

 Replace

by :
“Can computers pass the imitation
game?”
The Imitation Game :
 Judge
talks to a man and woman
through teletype and has to
decide which is which.
 Turing : What if the man is
replaced by a computer?
 Passing the test = the judge
cannot do better than guessing.
What is the test for?
 What

is the purpose?
One proposal : provides a
(behavioral) definition of thinking
 Probably

not :
Turing thought that the question of
whether machines can think is
“too meaningless to deserve
discussion”.
A bad definition anyway
 Definition
: X = ABC
 In a correct definition, ABC are
the necessary and sufficient
conditions for X.
 Passing the test is neither
necessary nor sufficient for
thinking.
Passing not necessary
 Things
that think, but which fail
the test :
Systems that can think but cannot
communicate with a language, or
too shy or paranoid to do so.
 The judge might be a computer
expert who can detect subtle
hints.

Turing on clever judges
 Turing
recognized an objection
similar to the last point.
 He said that "we need not be
troubled" as long as there are
machines that can pass the test.
 So he did concede that passing
the test is not necessary for
being able to think.
Also not sufficient
 Things
that cannot think, but
pass the test :
Blockhead : a stupid machine that
stores all possible conversations
within some limited duration.
 Blockhead is logically possible,
but not practically possible.

Blockhead
 Ned
Block “The Mind as the
Software of the Brain”
All possible
opening lines
from the judge
All possible
replies
Proposal
 The
test is a practical
sufficiency test for intelligent
thinking.
 Often taken as a practical goal
for AI.
 Allows for thinking computers
that fail the test.
Other issues
 Problems

with judges
Who can be a judge? What if a
computer passes the test because
of a stupid judge?
Real tests

The Loeber Prize