Philosophy and Cogsci The Turing Test Joe Lau

Alan Turing ( ) n Famous British mathematician / logician n Mathematical theory of computation. n Helped cracked the German U- boat Enigma code in WWII. n A homosexual, arrested in n Committed suicide.

More information n More on Turing’s life : n Turing’s biographer Andrew Hodges : n Computation theory n Book : Boolos and Jeffrey’s Computability and Logic n Article : in Stanford Encyclopaedia of Philosophy (web)

Topic n 1950 paper in Mind “Computing Machinery and Intelligence” n Introduced computers to philosophy n Argued for the plausibility of thinking machines n Proposed “Turing test” often cited as criterion of success for AI.

Turing’s Proposal n The question “Can machines think?” is too vague. n What are machines? n What is thinking? n Replace by : n “Can computers pass the imitation game?”

The Imitation Game : n Judge talks to a man and woman through teletype and has to decide which is which. n Turing : What if the man is replaced by a computer? n Passing the test = the judge cannot do better than guessing.

What is the test for? n What is the purpose? n One proposal : provides a (behavioral) definition of thinking n Probably not : n Turing thought that the question of whether machines can think is “too meaningless to deserve discussion”.

A bad definition anyway n Definition : X = ABC n In a correct definition, ABC are the necessary and sufficient conditions for X. n Passing the test is neither necessary nor sufficient for thinking.

Passing not necessary n Things that think, but which fail the test : n Systems that can think but cannot communicate with a language, or too shy or paranoid to do so. n The judge might be a computer expert who can detect subtle hints.

Turing on clever judges n Turing recognized an objection similar to the last point. n He said that "we need not be troubled" as long as there are machines that can pass the test. n So he did concede that passing the test is not necessary for being able to think.

Also not sufficient n Things that cannot think, but pass the test : n Blockhead : a stupid machine that stores all possible conversations within some limited duration. n Blockhead is logically possible, but not practically possible.

Blockhead n Ned Block “The Mind as the Software of the Brain” All possible opening lines from the judge All possible replies

Proposal n The test is a practical sufficiency test for intelligent thinking. n Often taken as a practical goal for AI. n Allows for thinking computers that fail the test.

Other issues n Problems with judges n Who can be a judge? What if a computer passes the test because of a stupid judge?

Real tests n The Loeber Prize