3. According to the substance dualist, there are two kinds of substances: physical substances and mental substances.

4. Physical substances have physical properties:  Size  Shape  Location  Mass  Charge  Spin, etc.

5. Mental substances have mental properties [mental states]:  Emotions  Sensations  Perceptions  Thoughts  Moods

6. The substance dualist thinks that no physical substance has mental properties and no mental substance has physical properties. Minds don’t have size, shape, location, etc. and brains don’t have moods, thoughts, pains, etc.

9. The robot can’t be sentient (have a mind), because robots can’t _____: Things with minds can _____ Robots can’t ______ Therefore, no robot has a mind.

10.  Be expressive  Exhibit curiosity  Engage in playfulness  Speak fluidly  Learn new things  Appreciate beauty  Expect future conscious experiences

11.  Have a fear of death  Act originally  Enjoy dancing and music  Have a sense of humor  Conform to moral laws out of principle  Mentally associate disparate things  Exhibit spontaneous emotional responses

12. Similar arguments can be made for substance dualism. Instead of “Robots can’t _____,” the substance dualist argues that there are things minds can do that “No physical object can _____”: Minds can _____ No physical object can _____ Therefore, no physical object is a mind.

13. Is it possible for physical objects to do these sorts of things– learn new things, be creative and original, fear death, make plans for the future, experience redness…?

22. René Descartes (1596-1650) was a French natural philosopher and mathematician. He is the father of modern (Western) philosophy, and he argued for substance dualism.

23. Descartes famously said “I think, therefore I am” (“Cogito ergo sum”). He argued that it is not possible for him to doubt his own existence. Only things that exist can doubt.

24. But Descartes thought it was possible for him to doubt that he had a body. Sure, it looks and feels like he has a body. But couldn’t an all-powerful God make it seem like Descartes had a body, when he really didn’t?

25. 1. I cannot doubt that I exist. 2. I can doubt that my body exists. 3. Therefore, I am not my body. 4. I am my mind. 5. Therefore, my mind is not my body

26. Gottfried Wilhelm Leibniz (1646-1716), like Descartes, was a natural philosopher and mathematician. Among his many achievements, he formulated a law of logic called Leibniz’s Law.

27. Also known as “the indiscernibility of identicals” If X = Y, then X and Y have all the same properties. [Converse] If X and Y don’t have all the same properties, then X ≠ Y.

28. Property: being red 1. My car is red (has the property of being red. 2. That car is not red (does not have the property) 3. Since my car and that car don’t have all the same properties, that car is not my car.

29. Property: being a thing whose existence Descartes can doubt. 1. Descartes’ body has the property of being a thing whose existence Descartes can doubt. 2. Descartes does not have the property of being a thing whose existence Descartes can doubt. 3. Therefore, Descartes is not Descartes’ body.

30. How we can know that there are minds other than our own?

31. The problem of other minds is the question of how we can know that there are minds other than our own. What is the cause of the problem?

32. We each experience our own minds directly, from ‘within’. I can know what I want or believe through introspection. I can neither have any phenomenological experience of other people’s mental states; nor can I know them through introspection. At first sight, at least, all we have to go on is other people’s behaviour, what is expressed through their bodies. If minds and bodies are entirely independent, then how can I infer from seeing a body that there is a mind ‘attached’? Other ‘people’ – other bodies – could all be machines, programmed to behave as they do, but with no minds.

34. Write down three signs that something has a mind Can you tell if something has a mind by how it behaves?

36. The argument from analogy (1) People are made of the same stuff as me and People behave very much as I do in similar circumstances; I have a mind; by analogy, it’s logical to think they do as well. It is perhaps the ‘commonsense’ position on how to solve the problem of other minds.

37. But we can object to its use of induction. The conclusion that other people have minds is based on a single case – mine. This is like saying ‘that dog has three legs; therefore, all dogs have three legs’. You can’t generalize from one case, because it could be a special case. Perhaps I am the only person to have a mind (solipsism).solipsism

38. The argument from analogy (2) A J Ayer reformulated the argument to avoid induction from one case by moving from a single correlation between ‘behaviour’ and (a single) ‘mind’ to correlating many behaviours of mine with many mental states of mine. This behaviour is correlated with this mental state; that behaviour with that mental state; and so on. Furthermore, mental states are causes of behaviour – to establish this, we only need our own case. But having established the cause, we may legitimately infer that the behaviour of others is caused by mental states.

39. But the argument relies on the view that like effects (behaviour) have like causes (mental states), a claim which has been generally rejected. Even if my behaviour is caused by my mental states, the behaviour of other people could be caused by something entirely different (say, brain states without mental states).

40. Inference to the best explanation Rather than inferring from one’s own case to other minds, we may employ a standard form of theoretical scientific reasoning, inference to the best explanation. What hypothesis best explains other people’s behaviour? The hypothesis that other people have minds, and that their mental states cause them to behave as they do.

41. Is this is a better hypothesis than the claim that (other) people are machines without minds? One way philosophers have developed the argument is to define mental states as the inner states of an organism that respond to the environment and cause behaviour (functionalism). The theory that there are such ‘inner’ states that cause behaviour is then said to be the best explanation of behaviour. Pain makes you respond quickly to prevent further damage; desire makes you pursue something you need; belief gives you information you need in order to pursue desires.

42. First, it depends on functionalism being the right account of what mental states are. But philosophers have argued that functionalism is neither the right account of thought nor of consciousness. Second, if we understand the mind in terms of its causal relations to behaviour, then we need to solve the problem of how the mind can cause physical events. Third, we can object that the belief that other people have minds is not a hypothesis, nor do we infer, on the basis of evidence, that they have minds. This argument is developed next.

43. Our experience presupposes other minds: on ascribing mental states A third solution is to reject the idea that we need to infer, in any way, that other people have minds. We can develop this claim in two ways. First, Wittgenstein argued that we react to people as minded, just as we react to them as alive, and this reaction is deeper, more fundamental than any beliefs about them. Our ‘belief’ that other people have minds, then, is not the product of any process of thought (including inference); it is part of human nature, which guides how we think.

44. Our experience presupposes other minds: on ascribing mental states He also argued that we can have direct awareness of other people’s mental states, most particularly, emotions. We can literally see anger in their facial expression, for example. Again, this is not a process of inference; the ‘interpretation’ is part of our perception of human faces itself. We experience the mind directly in bodily expressions. This particular response is not easily available to substance dualism, which holds that there is always a logical gap between anything bodily and a mental state.

45. Our experience presupposes other minds: on ascribing mental states A different approach argues that to have a mind oneself presupposes interaction with other minds. Descartes assumes that we can ascribe mental states to ourselves. But what does this ability require? We can argue that, for instance, a child cannot learn that it is angry without also learning what it means to say, of someone else, that they are angry.

46. Our experience presupposes other minds: on ascribing mental states The ability to ascribe mental states to oneself is learned, and is interdependent with the ability to ascribe mental states to other people. To learn the meaning of ‘anger’ is to learn its correct application to both oneself and others, simultaneously. In general, a sense of self (of oneself as a self) develops as part of the same process as the sense of others as selves. If there can be no knowledge of oneself as a mind without presupposing that there are other minds, the problem does not arise.

47. SOLIPSISM Descartes argues that he knows ‘I think’ before he knows anything else. He later remarks that he knows, too, what he thinks when he thinks it, e.g. he can identify a sensation of cold without mistake. In thinking about and identifying my experiences, I unite them under concepts. If nothing but me and my thoughts exist, then I need to be able to do all this, in language, without depending on anything else. Descartes’ knowledge argument supposes that we can make sense of the idea of our minds existing on their own, independently of anything outside. The idea that only my mind exists is solipsism.

48.  MAN: Pussy pussy pussy... coochicoochicoochi... pussy want his fish? Nice piece of fish... pussy want it? Pussy not eat his fish, pussy get thin and waste away, I think. I imagine this is what will happen, but how can I tell? I think it's better if I don't get involved. I think fish is nice, but then I think that rain is wet so who am I to judge? Ah, you're eating it. I like it when I see you eat the fish, because in my mind you will waste away if you don't.  Fish come from far away, or so I'm told. Or so I imagine I'm told. When the men come, or when in my mind the men come in their six black shiny ships do they come in your mind too? What do you see, pussy? And when I hear their questions, all their many questions do you hear questions? Perhaps you just think they're singing songs to you. Perhaps they are singing songs to you and I just think they're asking me questions. Do you think they came today? I do. There's mud on the floor, cigarettes and whisky on my table, fish in your plate and a memory of them in my mind. And look what else they've left me. Crosswords, dictionaries and a calculator.

49.  I think I must be right in thinking they ask me questions. To come all that way and leave all these things just for the privilege of singing songs to you would be very strange behaviour. Or so it seems to me. Who can tell, who can tell.....  MAN: I think I saw another ship in the sky today. A big white one. I've never seen a big white one. Only six small black ones. Perhaps six small black ones can look like one big white one. Perhaps I would like a glass of whisky. Yes, that seems more likely...  Perhaps some different people are coming to see me.  MAN: Hello?  FORD PREFECT: Er, excuse me, do you rule the Universe?  MAN: I try not to. Are you wet?

50.  FORD: Wet! Well, doesn't it look as if we're wet?  MAN: That's how it looks to me, but how you feel about it might be a different matter. If you find warmth makes you feel dry you'd better come in.  ZAPHOD BEEBLEBROX: Er, man, like what's your name?  MAN: I don't know. Why, do you think I ought to have one? It seems odd to give a bundle of vague sensory perceptions a name.  ZARNIWOOP: Listen. We must ask you some questions.  MAN: All right. You can sing to my cat if you like.  ARTHUR DENT: Would he like that?  MAN: You'd better ask him that.  ZARNIWOOP: How long have you been ruling the Universe?  MAN: Ah, this is a question about the past is it?

51.  ZARNIWOOP: Yes.  MAN: How can I tell that the past isn't a fiction designed to account for the discrepancy between my immediate physical sensations and my state of mind?  ZARNIWOOP: Do you answer all questions like this?  MAN: I say what it occurs to me to say when I think I hear people say things. More I cannot say..  ZARNIWOOP: No. Listen. People come to you, yes?  MAN: I think so.  ZARNIWOOP: And they ask you to take decisions—about wars, about economies, about people, about everything going on out there in the Universe?

52.  MAN: I only decide about my Universe. My Universe is what happens to my eyes and ears. Anything else is surmise and hearsay. For all I know, these people may not exist. You may not exist. I say what it occurs to me to say.  ZARNIWOOP: But don't you see? What you decide affects the fate of millions of people.  MAN: I don't know them, I've never met them. They only exist in words I think I hear. The men who come say to me, say, so and so wants to declare what we call a war. These are the facts, what do you think? And I say. Sometimes it's a smaller thing....  MAN: But it's folly to say you know what is happening to other people. Only they know. If they exist.  ZARNIWOOP: Do you think they do?  MAN: I have no opinion. How can I have?

53.  ZARNIWOOP: I have.  MAN: So you say—or so I hear you say.  ZARNIWOOP: But don't you see that people live or die on your word?  MAN: It's nothing to do with me, I am not involved with people. The Lord knows I am not a cruel man.  ZARNIWOOP: Ah! You say... the Lord! You believe in...  MAN: My cat. I call him the Lord. I am kind to him.  ZARNIWOOP: All right. How do you know he exists? How do you know he knows you to be kind, or enjoys what you think of as your kindness?  MAN: I don't. I have no idea. It merely pleases me to behave in a certain way to what appears to be a cat. What else do you do? Please I am tired.

54.  SOLIPSISM The arguments from analogy and inference to the best explanation assumed that there were other people, or other people’s bodies, and we needed to explain their behaviour. Solipsism would reply that there are no other bodies, only my experiences of other bodies. So those answers to the problem of other minds leave solipsism untouched. But the third response, the argument from ascribing mental states, provides an answer, as it entails that it is impossible to give an account of the mind, even one’s own mind, starting just from one’s own case. Solipsism supposes that my thoughts exist independently of anything else. But I could not have these thoughts without other minds existing.

55. From Descartes’ starting point emerges a picture of concepts and language that John Locke explicitly endorsed: ‘Words in their primary or immediate signification, stand for nothing but the ideas in the mind of him that uses them’. ( An Essay Concerning Human Understanding, III.ii.2) What I mean by ‘red’, for instance, is not, directly, the colour of the tomato, but the sensation I have of the colour of the tomato, or remember or imagine having. How does ‘red’ get its meaning? It’s as though I associate the word with the sensation, saying the word ‘red’ in my head, while keeping the sensation of red in mind as I do so. It is like pointing to a colour chart, but where the chart and the pointing are mental, not physical.

56. Your sensations, of course, are yours alone; they cannot be experienced by anyone else. This means that what you mean by words is given by something that no one else has access to. Your language is a ‘private’ language, meaning it is logically impossible for anyone else to get at what you mean by words. Locke accepts this: for communication to occur, we must each mean similar sensations by the same words. Your ‘red’ must be similar to my ‘red’.

57. Wittgenstein argued that if this understanding of language were right, then solipsism would be inescapable. If all words get their meaning by referring to my experience, then what I mean by ‘experience’ means ‘my experience’. We have said that it is logically impossible that anyone else could have my experiences. But that means that it makes no sense to think of other people having experience – because ‘experience’ refers to my experience alone. But if no one else has experience, then solipsism is true. First, if it were true, we could not understand each other. Locke says that the sensations to which we privately refer would have to be similar. But this comparison is impossible; in fact, it makes no sense. If meanings are given by private sensations, there is no meaning to the phrase ‘my sensations are similar to yours’. I cannot meaningfully refer to your sensations or compare them with mine.

58.  Second, words would not have meaning at all. How do I associate a word to a sensation? We suggested it was like mentally pointing at a mental sample. Wittgenstein argues this is not enough. Meanings are stable, and words can be used correctly or incorrectly. If ‘red’ means the sensation that comes to mind when I think of the word ‘red’, how can I check if the right sensation has come to mind?  For instance, can I tell if it is the same sensation that occurred when I first labelled the sensation ‘red’? I try to recall that sensation – but of course, this is just to think again of what I mean by ‘red’. I’m not comparing two things at all, so I can’t check one against the other. Putting the point another way: what is it to remember correctly the sensation I originally associated with the word ‘red’? It is to remember the same sensation. What do I mean by ‘the same sensation’? Well, the sensation of red. But this is a vicious circle. We were trying to fix the meaning of the word ‘red’ by appealing to a sensation. But now we have to appeal to the meaning of red to identify the correct sensation!

59. Why does this matter? Because there is no gap between what seems right (I think it is the same sensation) and what is right (it being the same sensation). This means I can’t use the word ‘wrongly’ – ‘red’ is whatever occurs to me at the time I’m thinking. But words can be used wrongly, i.e. with the wrong meaning. So this cannot be how words get their meaning. Wittgenstein concludes that we cannot fix the meaning of words by appealing to private sensations. Instead, we have to use something public, available to other people. For example, we might fix the meanings of colour words by using a colour chart. This defeats solipsism, since, as we saw, that presupposes that the meanings of words can be fixed by reference to my experiences alone. If this is logically impossible, solipsism literally makes no sense.