Turing begins his paper with a description of a set of rules for a test he calls the “imitation game,” (what would later come to be known as the Turing Test) as a means of answering the question, “can machines think?” In the game, there is an interrogator, a man, and a woman. The object of the game for the interrogator is to determine who the man is and who the woman is only by asking each of them questions. The questions are administered in such a way that the interrogator gleans no additional information from them besides the answers themselves – for example, through the passing of typed notes. The argument suggested by Turing in the paper is that if the man or the woman were replaced by a machine and the interrogator finds it equally difficult to distinguish between human and computer, then it can be said that the machine in question “can think.”

In the next section of his paper, Turing discusses possible criticisms of the new way in which he has framed the question. He argues that his proposed method factors out the physical appearance of a machine in our perception of whether or not it can think, and that “[t]he question and answer method seems to be suitable for introducing almost any one of the fields of human endeavour that we wish to include.” He argues that even though it seems as if the game heavily favors the human (it’s very difficult for a human to trick someone into thinking they are a computer, too), this doesn’t matter as long as one can accept that it is possible for a machine to be built that can take this test.

In the next few sections of the paper, Turing further clarifies the definition of a “machine” in his description of the game to mean “digital computer” and then goes on to describe various qualities of digital computers. He discusses the elements of a digital computer (“store,” “executive unit,” and “control”) and describes their finite state nature. A reference is made to Babbage’s Analytical Engine as an example of a machine that is a digital computer despite not being an electronic one. A section is also spent arguing that because of the finite state nature of a digital computer, it is possible for a digital computer to simulate any discrete-state machine. This implies that if any one machine can be constructed to play the imitation game, it answers the broader question of “can machines think.”

These sections specifying the machine described in the original outline of the imitation game are followed by a list of possible arguments in opposition to the claim that it is possible to construct a machine that can think. These arguments and my brief interpretations of Turing’s responses to them are as follows:

  1. “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.”

Turing’s response: If God is truly an omnipotent being, then should it not be within his power to assign a soul to an animal, or, similarly, to a machine, and thus also give the power to think?

2. “The consequences of machines thinking would be too dreadful. Let us hope and believe that they cannot do so.”

Turing’s response: This argument is so trivial that it needn’t even be considered.

3. Mathematics has shown that there are problems which cannot be solved mathematically. Doesn’t this mean that there are problems which can’t be solved by digital computers as discrete state machines, which could be solved by humans?

Turing’s response: Although this is a strong argument, do we assign too much importance to our ability to answer questions that a machine theoretically cannot? Those that make this argument would be okay with discussion the question through the criteria of the imitation game anyway.

4. Unless a being can express emotions and be conscious of these emotions, it cannot be said that this being can think.

Turing’s response: It’s possible to test this quality using the imitation game – saying a machine has been programmed such that it writes a poem. It’s possible to for an interrogator to ask questions about the poem to assess whether the machine was conscious of its decisions in the writing of the poem.

5. There will be things that a machine cannot do (“…be kind, resourceful, beautiful, friendly…”).

Turing’s response: This is simply an issue of storage capacity – given infinite storage capacity, machines can have a large diversity of behaviors.

6. Machines can only do what they are programmed to do – they cannot exhibit some behavior that was not already defined in the programming.

Turing’s response: What this argument is really suggesting is that machines cannot surprise. Can it really be said that humans are capable of new thought, if all their ideas are based on things that they have learned?

7. The nervous system is not a discrete state machine – it is continuous. How can a computer simulate human thought as a discrete state machine then?

Turing’s response: A digital machine can simulate a continuous machine so closely that the difference will not be clear to the interrogator in the imitation game.

8. There is no set of rules which can describe what a person should do for every possible scenario.

Turing’s response: Although it may be difficult to comprehend, we cannot say for sure that there is not one set of rules which can be used to predict all of our behavior. Even in a simple case where a computer is given a number and then returns another with no indication of what it has done, it is difficult or impossible to guess the rule that will predict every possible output – that does not mean that one does not exist.

9. A machine cannot exhibit extra-sensory perception.

Turing’s response: In this case, a special imitation game will have to be set up with a “telepathy-proof room” to be sure that the machine is not being influenced by psycho-kinetic powers.

In the final section of the paper, Turing again addresses oppositional argument number 6 – Ada Lovelace’s argument that a computer can only do what it has been programmed to do. Turing discusses a process which he believes could overcome the difficulty in programming a machine that could successfully pass the imitation game as well as disprove the Ada Lovelace argument. In this process, rather than trying to program a fully functional machine from the start, it might be better to create a “learning machine” – a machine that begins with only a base set of rules and then continually updates these rules of interaction as it learns.