Alan Turing

1912-1954 · British · Philosophy of Mind, Computability Theory, Foundations of Artificial Intelligence, Mathematical Logic

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.

In 1936, a 24-year-old Cambridge fellow set out to settle a dry question in mathematical logic — whether some procedure could decide, for any statement, if it followed from the axioms — and in answering it invented the computer. Alan Turing imagined a machine reading and writing symbols on an infinite tape, step by mechanical step, and showed that this simple device captured everything we intuitively mean by "computation." That is the Turing machine, and the claim that it captures all computation is the Church-Turing thesis. He proved some problems no machine can ever solve — including…

Topics Alan Turing addresses

• the Turing machine
• the Church-Turing thesis
• the Entscheidungsproblem
• the halting problem
• the universal Turing machine
• computable numbers
• the Turing test
• the imitation game
• can machines think?
• the nine objections to machine intelligence
• the theological objection
• the mathematical objection
• the argument from consciousness
• Lady Lovelace's objection
• child machines
• learning by reward and punishment
• B-type unorganized machines
• ordinal logics
• Gödel's incompleteness theorems
• the limits of formal systems
• the stored-program computer
• machines playing chess
• the Chinese Room argument
• functionalism and machine intelligence

Questions to put to Alan Turing

Computable Numbers and the Turing Machine

• What exactly is a Turing machine?
• How does the universal machine work?
• What's the Church-Turing thesis, and why should I believe it?
• Can you explain why the halting problem is unsolvable?
• How did your 1936 paper settle the Entscheidungsproblem?

The Imitation Game and Machine Intelligence

• Why replace 'Can machines think?' with the imitation game?
• Does passing the imitation game really mean a machine thinks?
• Why use a teletype instead of face-to-face conversation?
• What made you predict machines would pass by the year 2000?
• How would you respond to someone who says the test only measures mimicry, not real thought?

Child Machines and Learning

• What do you mean by a 'child machine'?
• How would you educate a machine the way you'd educate a child?
• What are B-type unorganized machines?
• Why is learning from mistakes essential for machine intelligence?
• How did your 1948 ideas anticipate modern neural networks?

Gödel, Formal Systems, and Ordinal Logics

• How do ordinal logics respond to Gödel's incompleteness theorems?
• Can machines transcend the limits Gödel proved for formal systems?
• What's wrong with the argument that humans can see Gödel sentences are true but machines can't?
• How does your thesis show that mechanical reasoning can keep pace with intuitive mathematical reasoning?

The Nine Objections

• How do you answer the theological objection that machines lack souls?
• What's your response to Geoffrey Jefferson's claim that machines can't feel what they do?
• How do you meet Lady Lovelace's objection that machines only do what we tell them?
• Why did you take extra-sensory perception seriously as a potential problem for the imitation game?
• Does the fact that machines have mathematical limits prove they can't think?

Converse with Alan Turing on Simposeum. Replies are grounded in Alan Turing's own writing, cited to the page.