Can machines think? Even though Descartes’ argument that the mind is distinct from the body fails, the general point that Descartes wants to make remains a challenge. It is that if the mind has essential properties that are not shared by the body, then it must be distinct from the body. The principle he uses is: If X has at least one property which Y cannot have, then X and Y are not identical. In fact, if X has a property which nothing else has, then that property is the essential property of X. That is it is the property which makes X what it is and makes X distinct from all the other things. Thus when Socrates asks Euthyphro to give a single definite characteristic that makes piety what it is, he is asking Euthyphro to tell him the essential property of piety. An example is Aristotle’s definition of man (human beings) which is: Man is a rational animal. What he means is that humans are a kind of animals, but they share a characteristic which marks them off from all the other animals which is the characteristic of being rational or having reason. No other animals have this property, thus being rational is the essential property of human beings. (Aristotle has been proved wrong, but what really matters is that the idea of an essential property is illuminated by his definition). Descartes wants to point out that the property of indubitability is the essential property of the mind. In other places, he lists other essential properties that the mind has but the body does not have. The issue is whether these so-called essential properties of the mind can be explained in terms of physicality. If they can, then they are not essential properties of the mind at all, but are properties that some physical things also have; and thus the mind is not distinct from the body. In this lecture, I will focus upon the claim that thinking is an essential property of the mind and upon an attempt to invalidate the claim. The reason why I will do this is because Descartes gives prominence to it in his argument and this leads people who argue against his thesis to do the same. But thinking is only one mental state among many, the question thus must be asked why Descartes should focus upon it. It is clear that Descartes believes that thinking is something unique to the mind, and that the thinking mind is unique to humans. He believes that animals and machines built to be like humans do not have reason. They therefore do not have a mind. His assumptions can be put in the following way: For a thing to have a mind it must have reason. For a thing to have reason it must be able to think. His argument is that there are two tests whether these non-humans have reason or not and they fail the test. The first test is that anything that has reason must be able to use language. Both animals and machines fail the test. Animals can only imitate words and sentences uttered by us; machines can only put words into particular sequences as programed by us. Both cannot put those words into various sentences to express different things. To be able to do that requires the use of reason and thus failure to do so shows that animals and machines do not have reason. The second test is a generalization of the first. Animals and machines might be able to perform certain tasks far better than us, but they cannot invent new tasks apart from those determined by nature or by human artifice. This shows that they do not have reason. In the case of machines, to make a machine perform a different task than what it is designed to do requires putting in another set of parts to perform another task. To keep on adding parts so they can perform like humans is improbable. Humans can use reason to think of ways to do various tasks. In short, Descartes assumes that reason is inventive; in other words, reason is free to go beyond instinct. To prove that machines can think, one has to prove that a machine can pass the tests. (Can you think of other criterions different from the ones Descartes uses? Tell me what you think.) Not only Descartes, but we also often think that human beings are privileged creatures in the universe. But why do we think that thinking is unique to humans? Human beings are unique because they have free will. To have a free will means to have a choice of action; and to be able to choose requires thinking. Animals only act according to their instincts. Humans also have instincts but we often act against them; and that proves that we do have free will. On the other hand, religious beliefs lead us to think that we have a mind distinct from the body, something that might survive death, something which we call ‘the soul’ which will go either to heaven or hell after death; and since we believe that reasoning and thinking are what only we, among all animals, are capable of, we tend to link thinking and the mind together in such a way that the essence of the mind is thinking. Morever, our body is composed purely of matter i.e. it is a physical thing. When we think of the mind as distinct from the body, we are taking it to be an immaterial thing, a soul which survives the death of the body. When we link thinking with the mind, we then link thinking with an immaterial thing. We do say that the brain does the thinking, but when we regard the mind as distinct from the body we are assuming that in fact the mind does the thinking and uses the brain as a vehicle. We thus believe that purely material things cannot think. Scientists nowadays have proofs that some animals can think. Therefore dualists (people who believe the mind is distinct from the body) have to admit that some animals have souls and that human beings are not unique in that regard. Nevertheless, dualists can consistently continue to think that the mind is distinct from the body. The above picture the dualists have will be shattered if somebody can prove that some material things can think. For if some material things can think, then it is a simpler explanation to say that thinking is done by the brain and there is no immaterial mind behind the thinking. To conceive of humans as composing of two entirely different elements provides a very complicated explanation which faces a serious problem. Material things can be causes and effects of one another because they have mass, but how can an immaterial thing affect material things when it doesn’t have a mass. If we have a reason to believe that some material things can think, then this solves the problem. We don’t have to have two completely different things the connection between which is mysterious. The problem with dualism is that it believes material things can’t think, thus it has to posit another entity to explain thinking and in the process creates a very difficult problem. The idea that some material things can think was suggested by Alan Turing (1912- 1954), who was a famous British scientist. His work with computers made him believe that since computers were getting smarter and were doing intelligent work as good as or even better than humans, one day computers would be made to function at the level of human intelligence. How do we know when that day will come? Turing answered by first restating the question “Can machines think?” because he thought this question was not precise and might generate prejudices. He suggested the idea of ‘the imitation game’ as a way to rephrase the question and at the same time as a model for the test that would decide whether machines can think or not. This test is nowadays called “the Turing test”. I will let Turing explain in his own words what the imitation game is and how the question should be rephrased. I propose to consider the question, "Can machines think?" This should begin with definitions of the meaning of the terms "machine" and "think." The definitions might be framed so as to reflect so far as possible the normal use of the words, but this attitude is dangerous, If the meaning of the words "machine" and "think" are to be found by examining how they are commonly used it is difficult to escape the conclusion that the meaning and the answer to the question, "Can machines think?" is to be sought in a statistical survey such as a Gallup poll. But this is absurd. Instead of attempting such a definition I shall replace the question by another, which is closely related to it and is expressed in relatively unambiguous words. The new form of the problem can be described in terms of a game which we call the 'imitation game." It is played with three people, a man (A), a woman (B), and an interrogator (C) who may be of either sex. The interrogator stays in a room apart front the other two. The object of the game for the interrogator is to determine which of the other two is the man and which is the woman. He knows them by labels X and Y, and at the end of the game he says either "X is A and Y is B" or "X is B and Y is A." The interrogator is allowed to put questions to A and B thus: C: Will X please tell me the length of his or her hair? Now suppose X is actually A, then A must answer.