Wednesday, 11 July 2012

The Strange Case of The Rational Dentist

[From my book The Philosophy Gym. Apologies for unfixable formatting problems]

One of the most intriguing of philosophical puzzles concerns other minds. How do you know there are any? Yes, you’re surrounded by living organisms that look and behave much as you do. They even say they have minds. But do they? Perhaps other humans are mindless zombies: like you on the outside, but lacking any inner conscious life, including emotions, thoughts, experiences and even pain. What grounds do you possess for supposing that other humans (including even me) aren’t zombies? Perhaps less than you think.

At the dentist’s

The scene: a dentist’s surgery. Finnucane is prostrate in the dentists chair, his mouth stuffed with cottonwool balls. A balding and bespectacled dentist is poking at a filling at the back of Finnucane’s mouth.

Dentist: Is it safe?….Is it safe?
Finnucane: Aaaargh!
Dentist. No. It’s not safe. It’s dropped out altogether. Very inferior quality filling. I shall replace it. I’ll give you some pain-killer. Even though I don’t believe you feel pain.


Finnucane can’t believe what he’s hearing.

Dentist: That’s right. I don’t believe you feel pain. In fact I don’t believe you have a mind at all.

Finnucane squints.

Dentist: Why? Because I am The Rational Dentist, that’s why. I’m not like those other dentists. I believe only what it’s reasonable to believe. Open wide.

The dentist takes a long silver syringe from a tray and slowly inserts the needle into the soft flesh at the back of Finnucane’s mouth. Beads of moisture appear across Finnucane’s forehead and his eyes widen in panic.Gradually the pain starts to fade.

Dentist: Oh, I know what those other dentists say. They say [in mocking tones], “But of course I am justified in believing that my poor patient has a mind. I poke his gums with one of these. And observe. He sweats. He writhes. He cries out. Surely I have all the evidence I could possibly want that I’m dealing with another conscious being like myself. He even tells me he’s in pain.”

The dentist puts down the syringe and stares coldly at Finnucane.

Dentist: I’m not so easily fooled. All this so-called “evidence” is totally unconvincing.

The private mind

Finnucane is astonished. How could anyone fail to believe that others have minds? We would ordinarily consider such a person to be mad, dangerous even. Yet the dentist insists he is merely being rational. He peers at Finnucane.

Dentist: You’re looking quizzical. Allow me to explain. My argument is simple. First, I cannot directly witness what goes on in another’s mind. I can observe their outward behaviour. But I can’t observe what goes on inside their mind, if they have one. Their experiences, beliefs, emotions, pains and so on – all are hidden away. A mind is a private place. The most private place of all.

It seems the dentist is correct. Suppose, for example, that you take a bite out of a lemon. You experience an intense bitter taste. You are directly and immediately aware that that you are having this experience. While others may experience the same sort of taste, it’s impossible for you to verify this directly. You cannot, as it were, enter into another’s mind and observe what they are experiencing along with them. The experiences of others are necessarily hidden. 

The dentist fumbles with his drill. Finnucane watches nervously.

Dentist: Oh, I can guess what you would say were you mouth not stuffed with cotton wool balls: “But you don’t have to rely on my behaviour. What if you were to scan what’s going on in my brain? What if you put a fibre-optic probe in there, so that you could see my pain neurones firing? Then you would have direct evidence that I’m in pain.” That’s what you would say, correct?

Finnucane nods.

Dentist: Wrong again! I still wouldn’t have directevidence. For how do I know that this sort of neurone firing is accompanied by consciousness, by feelings of pain, in other human beings? Perhaps it’s only in my own case that brain activity is accompanied by mental activity. Open wide again.

The argument from analogy

The dentist places a plastic suction tube in Finnucane’s mouth and begins to drill.

Dentist: Now the other dentists, they admit all this. They say, [again, mockingly] “Okay, I admit you can’t have direct access to what’s going on in the mind of another. But it doesn’t follow that you don’t have good reason to believe others have minds. You do. Their behaviour provides you with excellent grounds for supposing this. Youknow in your own case that when you’re pricked sharply, you feel pain. You also know that when you experience that pain, you’re liable to flinch and yell. When you observe other human beings, you find that when they are pricked sharply, they also flinch and yell. Doesn’t that provide you with good grounds for supposing they experience pain too?”

The argument just outlined by the dentist is called the argument from analogy. At first sight, the argument looks highly plausible. Most of us, if asked to justify our belief in the existence of other minds, would no doubt offer something similar. But as the dentist is well aware, there’s a notorious difficulty with it.

A problem with the argument from analogy

Dentist: Open wider. Now of course I understand this argument. I’m not a fool. But I am afraid the logic is faulty. For you see, these other dentists are guilty of making an unwarranted generalization.

Finnucane is struggling to hear what the dentist is saying over the noise of the drill.

Dentist: Let me explain why. Suppose I cut open one thousand cherries and find every single one has a stone in the middle. Surely I’m now justified in generalizing. Surely I’m now justified in believing that allcherries have stones in the middle. Admittedly, I might be wrong. But the one thousand cherries that I have observed surely give me pretty good reason to believe that all cherries have stones, reason sufficient to justify my belief. Correct?

Finnucane nods.

Dentist: But now suppose that, instead of basing my inference on an observation of a thousand cherries, I base it on an observation of justone. Then my inference would be very shaky, wouldn’t it? My one cherry may provide some slight evidence in support of the claim that all cherries have stones, but it’s surely not enough to justify my making that generalization. For all I know, some cherries may have stones and some not, just as, for example, some animals have male sex organs and some not. This may be a very unusual cherry, just as an oyster with a pearl inside is very unusual. In order to justify my generalization, I surely need to look inside very many cherries. Correct?
Finnucane: Uh huh.
Dentist: But now think about the argument of the other dentists. It, too, is a generalization based on just a single observation. I notice that, in my own case, when I am pricked sharply and I flinch and yell, this behaviour is accompanied by pain. I am then supposed to conclude that when others are pricked sharply and they flinch and yell, they must be in pain too. Yes?
Finnucane: Uh huh.
Dentist: But one can’t justify the belief that others have minds on the basis of such flimsy evidence. This inference is surely no less suspect than the inference based on a single cherry. To infer that others have minds on such grounds is wholly unwarranted. It’s irrational. Being The Rational Dentist, I refuse to accept an irrational conclusion.

Scepticism about other minds

The dentist appears to be right. I can’t directly observe what goes on in the mind of another, or even that others have minds. So how might my belief in their existence be justified? Only, it seems, by the argument from analogy. But the argument from analogy is, in effect, a generalization based on a single observed case. So it’s just as shaky as the inference based on the single cherry.
The conclusion to which I seem forced, then, is that I am notjustified in believing that there are any minds other than my own. And if I am not justified in believing there are minds other than my own, then presumably I can’t be said to know that there are minds other than my own, for presumably it is a condition of knowing that there are other minds that I be justified in supposing my belief is true.
This is a sceptical conclusion: it says that I don’t know what I might think I know. This particular form of scepticism – scepticism about knowledge of other minds – has a long history. And of course, like most sceptical conclusions, it’s highly perplexing, for it runs entirely contrary to common sense. (You will find other forms of scepticism discussed in other chapters: chapter XX “Brainsnatched” discusses scepticism about the external world and chapter XX “Why Expect the Sun to Rise Tomorrow?” focuses on scepticism about the unobserved.)
So the sceptic leaves me in a paradoxical situation. On the one hand, it seems I have little if any reason to suppose there are other minds. On the other hand, this conclusion is so counter-intuitive that I suspect the sceptic must have gone wrong somewhere along the way. The challenge I face, then, is to identify what, if anything, is wrong with the sceptic’s argument.

[[TEXT BOX: THINKING TOOLS: How not to respond to scepticism. People commonly make one of two mistakes when presented with such seemingly compelling sceptical arguments.
First, they just dig in and dogmatically assert that of course they know that their’s is not the only mind – it’s “just obvious” that other minds exist. This is hardly an intelligent response, however. Sure, we feel certain that there are other minds. But simply to appeal to such feelings when presented with a sceptical argument is a mistake. What has previously struck us as “just obvious” has in many cases turned out to be wrong. That the Sun revolves about a stationary Earth, for example, was at one time considered by almost everyone to be “just obvious”. Consider how irritatingly irrational were those who continued brutely to insist that it is “just obvious” the Earth is stationary even after they had been presented with powerful evidence to the contrary. To similarly dismiss the sceptic’s argument would be no less irritatingly irrational.
The second mistake is blithely to accept the sceptic’s conclusion because one has underestimated its strength. It can be tempting to say, “Yes, yes, I agree with you that I can’t be certain that there are other minds. I admit I don’t know they exist. But still, it is pretty likelythat they exist, isn’t it?”
This is simply to misunderstand the argument. The sceptic is notarguing that, because there is room for doubt about the existence of other minds, therefore one can’t know that they exist. That would be a rather feeble argument, an argument based on the dubious assumption that one can’t be said to know something unless it has been established beyond all doubt. The dentist’s argument is much stronger. The dentist argues that not only is there room for doubt about the existence of other minds, there is actually little if any reason to suppose they exist. This is a much more dramatic conclusion, a conclusion that few if any of us really accept. END OF TEXT BOX]

Is the dentist rational, or insane?

The dentist leans over Finnucane again, his antiseptic-smelling breath fogging Finnucane’s glasses. He starts to work the new amalgum filling into the hole he has drilled in Finnucane’s molar.

Dentist: Perhaps you would say, “But why, if you don’t believe I have a mind, do you go to all the trouble of speaking to me, of administering anaesthetic, and so on?” The answer is: because I find that if I administer anaesthetic my patients don’t moan and thrash about. I use it to control behaviour. And I speak to them because I find it enables me to have some control over their behaviour. And also because it amuses me.

Finnucane raises his eyebrows.

Dentist: And of course, it is possible that you have a mind. I don’t deny that. So I give you the benefit of the doubt. I administer anaesthetic just in case.

Finally, after a few minutes, the filling is complete. Finnucane leans forward groggily, cotton wool balls tumbling from his mouth. He spits a bloody gobbet into the stainless steel tray. No longer at the dentist’s mercy, Finnucane finally feels free to speak his mind.

Finnucane: Good grief. You’re not the rational dentist. You’re the maddentist. Anyone who, like you, refuses to believe that others have minds, is, frankly, ill!
Dentist: It’s true that I’m often accused of suffering from some sort of mental illness. But my accusers are fools. For the truth is that I am merely being rational. I believe what it is reasonable to believe. And what is wrong with that?
Finnucane: You’re insane!
Dentist: It’s ironic, don’t you think, that you accuse me of being insane, when I’m the rational one?

The dentist is a bizarre character, frightening even[i]. We would find profoundly disturbing anyone who genuinely refused to believe that others have minds. In fact, scepticism about other minds is, for anyone not in the grip of some sort of mental illness, surely impossible to believe. The kind of disengagement from others required permanently to maintain the view that, for all you know, they are merely mindless automata is surely the hallmark of a kind of insanity.
And yet, for all that, the dentists’s seemingly “insane” sceptical position may be the rational position to adopt. Perhaps he is right that we’re the “irrational” ones. The onus is clearly on us to explain why belief in the existence of other minds is justified.
            Let’s now take a look at two well-known attempts to solve this puzzle. The first involves defending the argument from analogy.

1: Defending the argument from analogy

In response to the sceptical argument, you might point out that sometimes we are justified in generalizing on the basis of a single observed instance.
Suppose I decide to take my Kawazuki K1000 stereo apart to find out how it works.


I investigate its inner mechanism and establish how everything functions. Wouldn’t I then be justified in concluding that all stereos of that make and model have the same sort of internal mechanism? Surely I would. Yet this would be a generalization based on a single observed instance: my own stereo. And if we are sometimes justified in generalizing on the basis of a single observed case, then perhaps we are also justified in doing so when it comes to other minds. In which case the argument from analogy is sound after all.
            This is an interesting suggestion. But there are problems with it. True, it seems I am justified in believing that all Kawazuki K1000 stereos have such-and-such an internal mechanism on the basis of having opened up just one. But I am only justified because I am in possession of considerable background information about such devices and their inner workings. For example, I know that my Kawazuki K1000 stereo is a piece of machinery mass-produced for profit. I know that it takes a considerable investment in time and money to develop an inner mechanism of this sort. So I know that the Kawazuki Corporation is hardly likely to have bothered developing lots of different internal mechanisms to do the very same job. It’s because I possess this sort of background information that I am justified in believing that all the other Kawazuki K1000 stereos have the same sort of inner mechanism.
            However, I am not warranted in generalizing on the basis of a single observed case where such background information is missing. For example, if, for all I knew, each Kawazuki K1000 stereo might just as easily have been made, not by a single manufacturer, but by one of thousands of entrants in a competition to come up with internal machinery that would make these boxes marked “Kawazuki K1000” behave in just the way they do – raising the volume when this knob is turned, changing the radio station when that button is pressed, and so on – then of course I am no longer warranted in supposing that the other boxes will contain the same internal machinery.
            So the question is: do I possess the kind of background information necessary to justify my inference about the existence of other minds?
It seems not. In the stereo example, my inference depends on my background knowledge about mass-produced machines and their internal mechanisms. But in the case of other minds, I don’t appear to possess this sort of background knowledge. For my mind is radically unlike anything else I have ever experienced. For me to conclude that, as I have a mind, so too must other humans is akin to me entering a strange land, discovering that the first flower I examine contains a fairy, and then concluding that so too must all the other flowers. What I discover inside the first flower is so strange and unusual that no such inference is warranted.
It seems, then, that I’m still not justified in believing that there are minds other than my own.      

2: The logical behaviourist approach

Here is a different kind of solution to the puzzle of other minds, the solution offered by the logical behaviourist.
Consider the solubility of a sugar cube. Solubility is what is known as a dispositional property – its possession by a sugar cube just consists in the fact that if the cube were placed in water under the right circumstances, then it would dissolve. Indeed, it’s true by definition that something is soluble just in case it is disposed to dissolve in water, in just the same way that it is true by definition that all stallions are male or that all triangles have three sides.
Now some philosophers have suggested that mental properties are also dispositional properties. Indeed, some suggest that all talk about minds and what goes on in them can be translated, without residue, into talk about behavioural dispositions. This is the position of the logical behaviourist.
            Take pain, for example. To say that someone is in pain just is, according to the logical behaviourist, to say that they are physically disposed to behave in certain ways – to flinch, yell out, and so on. It’s true by definition that those in pain are disposed to behave like that. This is not something we need to discover.

            Logical behaviourism, if true, would neatly solve two classical philosophical problems concerning the mind. First of all, it would explain how material objects, such as our bodies, can possess minds. For an object to have a mind is just for it to possess the right sort of behavioural dispositions. That’s all there is to it. So we no longer have to make room for mysterious and ghostly extra “somethings” –  minds –  in the world, in addition to physical objects and their various physical dispositions. The “ghost in the machine”, to borrow the behaviourist Gilbert Ryle’s (1900-1976) memorable phrase, disappears.
            The other classical conundrum that would be solved is, of course, the one we have been discussing here: the problem of explaining how we come by knowledge of the existence of other minds. According to logical behaviourism, what makes the problem of other minds seem so intractable is a certain mistaken conception of what minds are like. If we think of the mind as the elusive “ghost in the machine”, then we are immediately struck by the problem of explaining how we establish the existence of this “ghost” in others. For all we can observe of other human beings is their outward behaviour. But if Ryle is right, the mind is not a peculiar ghostly “something” hidden behind the outward behaviour. Rather, the mind just is a highly complex set of behavioural dispositions.
Just as there is nothing particularly difficult about establishing what dispositional properties – such as solubility – a sugar cube has, so, if Ryle is right, there is nothing particularly difficult about establishing that human beings have minds. You need only establish how they are disposed to behave, and that can be done quite easily. Just as you can have good grounds for supposing that sugar cubes are soluble, so you can have good grounds for supposing that others feel pain.

Attack of the zombies

Has the logical behaviourist solved the problem of other minds? No. Unfortunately, logical behaviourism is not a particularly plausible theory of the mind. Perhaps the most serious difficulty with it is raised by theconceptual possibility of zombies.
In the movies, zombies drool and stumble about. The kind of zombies I have in mind are rather different: their behaviour is exactly the same as that of a minded person. Philosophical zombies, as I shall call them, behave perfectly normally. However, like movie zombies, philosophical zombies have no minds: they are, to borrow the dentist’s ugly phrase, “mere meat machines”.


Imagine a world physically exactly like this one but populated by zombies. This imaginary world even contains even a zombie version of you: just like you physically, but all is dark within. Of course, it’s not remotely likely that this zombie world actually exists. But (and this is the key point) we can at least make sense of the possibility of such a world.
Contrast the suggestion that there might be a world that contain non-male stallions or a world that contains triangles with four sides. These worlds don’t even make sense. For of course it is a definitional truth that stallions are male and that triangles have only three sides. Zombie world makes sense in the way that four-sided triangle world and non-male stallion world don’t.
But here’s the problem for logical behaviourism. If logical behaviourism is true, then it should no more make sense to suggest that zombie world might exist than it does to suggest that four-sided triangle world might exist. Just as it’s true by definition that a triangle has three sides, so it is supposed by the logical behaviourist to be true by definition that any creature that such-and-such behavioural dispositions has a mind. Zombies, being creatures that lack minds but have the same behavioural dispositions as ourselves, should be ruled out by definition.
But we have just seen that zombies are not ruled out be definition. But then it follows that logical behaviourism is false. And if logical behaviourism is false, then it can’t be used to solve the puzzle of other minds. The puzzle remains.

Most of us would say that Finnucane’s dentist is irrational, insane even. But perhaps it is we who are irrational, not the dentist. Can you rationally defend your belief that there are mind’s other than your own?
            I don’t yet see how.

What to read next?

Chapter XX “Brain-snatched” and chapter XX “Why Expect the Sun to Rise Tomorrow?” discuss other varieties of scepticism: scepticism about the external world and scepticism about the unobserved.

Further reading:

·      Anita Avramides, Other Minds (London: Routledge, 2001).
·      K. T. Maslin, An Introduction to the Philosophy of Mind (Cambridge: Polity, 2001), chpt. 8.

[i] In fact I have made the dentist slightly scarier than a sceptic need be. But I have tried not to over do it. I didn’t want the dentist to appear deliberately cruel and sadistic. After all, if the dentist clearly got some sort of perverse pleasure out of inflicting pain on Finnucane, that would suggest he did after all believe Finnucane had a mind worth torturing.

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