Think A Compelling Introduction to Philosophy

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  • Format: Hardcover
  • Copyright: 1999-10-14
  • Publisher: Oxford University Press
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The author of the bestselling "Oxford Dictionary of Philosophy" offers a coherent, non-intimidating introduction to the challenging and fascinating landscape of Western philosophy.

Author Biography

Simon Blackburn is the Edna J. Koury Distinguished Professor of Philosophy at the University of North Carolina, Chapel Hill. He was a Fellow and Tutor at Pembroke College, Oxford, from 1969 to 1990. His books for OUP are Spreading the Word (1984), Essays in Quasi-Realism (1993), The Oxford Dictionary of Philosophy (hbk 1994, pbk 1996), and Ruling Passions (1998). He edited the journal Mind from 1984 to 1990.

Table of Contents

Introduction 1(14)
Free Will
The Self
The World
What to Do
Notes 299(8)
Bibliography 307(4)
Index 311

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Chapter One


Perhaps the most unsettling thought many of us have, often quite early on in childhood, is that the whole world might be a dream; that the ordinary scenes and objects of everyday life might be fantasies. The reality we live in may be a virtual reality, spun out of our own minds, or perhaps injected into our minds by some sinister Other. Of course, such thoughts come, and then go. Most of us shake them off. But why are we right to do so? How can we know that the world as we take it to be, is the world as it is? How do we begin to think about the relation between appearance and reality: things as we take them to be, as opposed to things as they are?


We might say: it all began on 10 November 1619.

    On that date, in the southern German town of Ulm, the French mathematician and philosopher René Descartes (1596-1650) shut himself away in a room heated by a stove, and had a vision followed by dreams, which he took to show him his life's work: the unfolding of the one true way to find knowledge. The true path required sweeping away all that he had previously taken for granted, and starting from the foundations upwards.

    Of course, it didn't, really, begin in 1619, for Descartes was not the first. The problems Descartes raised for himself are as old as human thought. These are problems of the self, and its mortality, its knowledge, and the nature of the world it inhabits; problems of reality and illusion. They are all raised in the oldest philosophical texts we have, the Indian Vedas, stemming from about 1500 BC. The generation immediately before Descartes had included the great French essayist Montaigne, whose motto was the title of one of his great essays: `Que sais-je?'--what do I know?

    Nor did Descartes come to his enterprise with a totally innocent mind: he himself had an intense education in the prevailing philosophies of the time, at the hands of Jesuit teachers. But by Descartes's time things were changing. The Polish astronomer Copernicus had discovered the heliocentric (sun-centred) model of the solar system. Galileo and others were laying the foundations of a `mechanical' science of nature. In this picture the only substances in space would be material, made up of `atoms', and caused to move only by mechanical forces which science would eventually discover. Both Copernicus and Galileo fell foul of the guardians of Catholic orthodoxy, the Inquisition, for this scientific picture seemed to many people to threaten the place of human beings in the cosmos. If science tells us all that there is, what becomes of the human soul, human freedom, and our relationship with God?

    Descartes was smart. He invented standard algebraic notation; and Cartesian coordinates, which enable us to give algebraic equations for geometrical figures, are named after him. He himself was one of the leaders of the scientific revolution, making fundamental advances not only in mathematics but also in physics, particularly optics. But Descartes was also a pious Catholic. So for him it was a task of great importance to show how the unfolding scientific world--vast, cold, inhuman, and mechanical--nevertheless had room in it for God and freedom, and for the human spirit.

    Hence his life's work, culminating in the Meditations , published in 1641, `in which are demonstrated the existence of God and the distinction between the human soul and the body', according to the subtitle. But the subtext is that Descartes also intends to rescue the modern world view from the charge of atheism and materialism. The scientific world is to be less threatening than was feared. It is to be made safe for human beings. And the way to make it safe is to reflect on the foundations of knowledge. So we start with Descartes because he was the first great philosopher to wrestle with the implications of the modern scientific world view. Starting with the medievals or Greeks is often starting so far away from where we are now that the imaginative effort to think in their shoes is probably too great. Descartes is, comparatively, one of us, or so we may hope.

    There is a danger in paraphrasing a philosopher, particularly one as terse as Descartes. I am going to present some of the central themes of the Meditations . This is in the spirit of a sportscast showing only the `edited highlights' of a game. Closer acquaintance with the text would uncover other highlights; closer acquaintance with its historical context would uncover yet others. But the highlights will be enough to illuminate most of the central issues of subsequent philosophy.


There are six Meditations . In the first, Descartes introduces the `method of doubt'. He resolves that if he is to establish anything in the sciences that is `stable and likely to last' he must demolish all his ordinary opinions, and start right from the foundations.

    For he has found that even his senses deceive him, and it is `prudent never to trust completely those who have deceived us even once'. He puts to himself the objection that only madmen (`who say that they are dressed in purple when they are naked, or that their heads are made of earthenware, or that they are pumpkins or made of glass'--madmen were evidently pretty colourful in the seventeenth century) deny the very obvious evidence of their senses.

    In answer to that, he reminds us of dreams, in which we can represent things to ourselves just as convincingly as our senses now do, but which bear no relation to reality

    Still, he objects to himself, dreams are like paintings. A painter can rearrange scenes, but ultimately depicts things derived from `real' things, if only real colours. By similar reasoning, says Descartes, even if familiar things (our eyes, head, hands, and so on) are imaginary, they must depend on some simpler and more universal things that are real.

    But what things? Descartes thinks that `there is not one of my former beliefs about which a doubt may not properly be raised'. And at this stage,

I will suppose therefore that not God, who is supremely good and the source of truth, but rather some malicious demon of the utmost power and cunning has employed all his energies in order to deceive me. I shall think that the sky, the air, the earth, colours, shapes, sounds and all external things are merely the delusions of dreams which he has devised to ensnare my judgment.

This is the Evil Demon. Once this frightening possibility is raised, his only defence is resolutely to guard himself against believing any falsehoods. He recognizes that this is hard to do, and `a kind of laziness' brings him back to normal life, but intellectually, his only course is to labour in the `inextricable darkness' of the problems he has raised. This ends the first Meditation .


The second Meditation begins with Descartes overwhelmed by these doubts. For the sake of the inquiry he is supposing that `I have no senses and no body'. But:

Does it now follow that I too do not exist? No: if I convinced myself of something then I certainly existed. But there is a deceiver of supreme power and cunning who is deliberately and constantly deceiving me. In that case I too undoubtedly exist, if he is deceiving me; and let him deceive me as much as he can, he will never bring it about that I am nothing so long as I think that I am something. So after considering everything very thoroughly, I must finally conclude that this proposition , I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind.

This is the famous `Cogito, ergo sum': `I think, therefore I am.'

    Having saved his `self' out of the general seas of scepticism, Descartes now asks what this self is . Whereas formerly, he thought he knew what his body was, and thought of himself by way of his body, now he is forced to recognize that his knowledge of his self is not based on knowledge of his embodied existence. In particular, he is going to meet problems when he tries to imagine it. Imagination is a matter of contemplating the shape or image of a corporeal thing (a body, or thing extended in space). But at this stage, we know nothing of corporeal things. So `imagining' the self by imagining a thin or tubby, tall or short, weighty bodily being, such as I see in a mirror, is inadequate.

    So what is the basis of this knowledge of the self?.

Thinking? At last I have discovered it--thought; this alone is inseparable from me. I am, I exist--that is certain. But for how long? For as long as I am thinking. For it could be, that were I totally to cease from thinking, I should totally cease to exist.... I am, then, in the strict sense only a thing that thinks.

The inquiry now takes a slightly different course. Descartes recognizes that a conception of oneself as an embodied thing, living in an extended spatial world of physical objects, will come back almost irresistibly. And he realizes that the `I' he is left with is pretty thin: `this puzzling I that cannot be pictured in the imagination'. So `let us consider the things which people commonly think they understand most distinctly of all; that is the bodies we touch and see'. He considers a ball of wax. It has taste and scent, and a colour, shape, and size `that are plain to see'. If you rap it, it makes a sound. But now he puts the wax by the fire, and look:

[T]he residual taste is eliminated, the smell goes away, the colour changes, the shape is lost, the size increases; it becomes liquid and hot; you can hardly touch it, and if you strike it, it no longer makes a sound. But does the same wax remain? It must be admitted that it does; no one denies it, no one thinks otherwise. So what was it in the wax that I understood with such distinctness? Evidently none of the features which I arrived at by means of the senses; for whatever came under taste, smell, sight, touch or hearing has now altered--yet the wax remains.

Descartes glosses the result of this example as showing that there is a perception of the wax that is `pure mental scrutiny', which can become `clear and distinct' depending on how careful he is to concentrate on what the wax consists in. So, by the end of the second Meditation , he concludes:

I now know that even bodies are not strictly perceived by the senses or the faculty of imagination but by the intellect alone, and that this perception derives not from their being touched or seen but from their being understood; and in view of this I know plainly that I can achieve an easier and more evident perception of my own mind than of anything else.


How are we to read a piece of philosophy like this? We start by seeing Descartes trying to motivate his method of extreme doubt (also known as Cartesian doubt, or as he himself calls it, `hyperbolic', that is, excessive or exaggerated doubt). But is the motivation satisfactory? What exactly is he thinking? Perhaps this:

The senses sometimes deceive us. So for all we know, they always deceive us.

But that is a bad argument--a fallacy. Compare:

Newspapers sometimes make mistakes. So for all we know, they always make mistakes

The starting point or premise is true, but the conclusion seems very unlikely indeed. And there are even examples of the argument form where the premise is true, but the conclusion cannot be true:

Some banknotes are forgeries. So for all we know, they all are forgeries.

Here, the conclusion is impossible, since the very notion of a forgery presupposes valid notes or coins. Forgeries are parasitic upon the real. Forgers need genuine notes and coins to copy.

    An argument is valid when there is no way --meaning no possible way--that the premises, or starting points, could be true without the conclusion being true (we explore this further in Chapter 6). It is sound if it is valid and it has true premises, in which case its conclusion is true as well. The argument just identified is clearly invalid, since it is no better than other examples that lead us from truth to falsity. But this in turn suggests that it is uncharitable to interpret Descartes as giving us such a sad offering. We might interpret him as having in mind something else, that he regrettably does not make explicit. This is called looking for a suppressed premise --something needed to buttress an argument, and that its author might have presupposed, but does not state. Alternatively we might reinterpret Descartes to be aiming at a weaker conclusion. Or perhaps we can do both. The argument might be:

The senses sometimes deceive us. We cannot distinguish occasions when they do from ones when they do not. So for all we know, any particular sense experience may be deceiving us.

This seems to be a better candidate for validity. If we try it with banknotes and forgeries, we will find that the conclusion seems to follow. But the conclusion is a conclusion about any particular experience. It is no longer the conclusion that all our experience (en bloc, as it were) may be deceiving us. It is the difference between `for all we know any particular note may be a forgery' and `for all we know all notes are forgeries'. The first may be true when the second is not true.

    Still, perhaps at this stage of the Meditations the weaker conclusion is all Descartes wants. But we might also turn attention to the second premise of this refined argument. Is this premise true? Is it true that we cannot distinguish occasions of error--things like illusions, delusions, misinterpretations of what we are seeing--from others? To think about this we would want to introduce a distinction. It may be true that we cannot detect occasions of illusion and error at a glance . That is what makes them illusions. But is it true that we cannot do so given time ? On the contrary, it seems to be true that we can do so: we can learn, for instance, to mistrust images of shimmering water in the desert as typically misleading illusions or mirages--tricks of the light. But worse, the fact that we can detect occasions of deception is surely presupposed by Descartes's own argument. Why so? Because Descartes is presenting the first premise as a place to start from--a known truth. But we only know that the senses sometimes deceive us because further investigations--using the very same senses-- show that they have done so. We find out, for instance, that a quick glimpse of shimmering water misled us into thinking there was water there. But we discover the mistake by going closer, looking harder, and if necessary touching and feeling, or listening. Similarly, we only know, for instance, that a quick, off-the-cuff opinion about the size of the Sun would be wrong because further laborious observations show us that the Sun is in fact many times the size of the Earth. So the second premise only seems true in the sense of `we cannot distinguish at a glance whether our senses are deceiving us'. Whereas to open the way to Descartes's major doubts, it would seem that he needs `we cannot distinguish even over time and with care whether our senses are deceiving us'. And this last does not seem to be true. We might try saying that the senses are `self-corrective': further sense experience itself tells us when a particular sense experience has induced us to make a mistake.

    Perhaps anticipating this kind of criticism Descartes introduces the topic of dreams. `Inside' a dream we have experiences which bear some resemblance to those of ordinary living, yet nothing real corresponds to the dream. Is Descartes's idea here that the whole of experience may be a dream? If so, once again we might use a distinction like the one we just made: perhaps we cannot distinguish immediately or `at a glance' whether we are dreaming, but using our memory, we seem to have no trouble distinguishing past dreams from past encounters with reality.

    Still, there is something troubling about the idea that all experience might be a dream. For how could we set about determining whether that is true? Sometimes people `pinch themselves' to ensure that they are not dreaming. But is this really a good test? Might we not just dream that the pinch hurts? We might try from within a dream to discover whether it is a dream. Yet even if we think up some cunning experiment to determine whether it is, might we not just dream that we conduct it, or dream that it tells us the answer that we are awake?

    We might try saying that events in everyday life exhibit a scale and a sheer coherence that dreams do not exhibit. Dreams are jerky and spasmodic. They have little or no rhyme or reason. Experience, on the other hand, is large and spacious and majestic. It goes on in regular ways--or at least we think it does. However, it is then open for Descartes to worry whether the scale and coherence is itself deceptive. That takes him to the Evil Demon, one of the most famous thought-experiments in the history of philosophy. It is a thought-experiment designed to alert us to the idea that, so far as truth goes, all our experience might be just like a dream: totally disconnected from the world.

    It is important to seize on two things at the outset. First, Descartes is perfectly well aware that as active, living, human agents we do not bother ourselves about such an outlandish possibility. In fact, we cannot: as many philosophers have pointed out, it is psychologically impossible to keep doubt about the external world alive outside the study. But that does not matter. The doubt is worth bothering about because of the task he is engaged upon. This is the task of finding foundations of knowledge, of ensuring that his beliefs are built on a sound footing. Descartes's inquiry is made for purely intellectual reasons. Second, Descartes is not asking you to believe in the possibility of the Evil Demon. He is only asking you to consider it--en route to getting clear how to dismiss it. That is, he thinks (not unreasonably, surely?) that unless this possibility can be dismissed, there remains a challenge of scepticism : the possibility that we have no knowledge, but that all our beliefs are entirely delusive.

    We can appreciate the thought-experiment by reminding ourselves how very `realistic' a virtual reality can become. Here is an updated variant of the thought-experiment. Imagine an advance in science that enables a mad scientist to extract your brain, and then to maintain it in a vat of chemicals that sustain its normal functioning. Imagine that the scientist can deliver inputs to the normal information channels (the optic nerve, the nerves that transmit sensations of hearing and touch and taste). Being good-natured, the scientist gives information as if the brain were lodged in a normal body and living a reasonable life: eating, playing golf, or watching TV. There would be feedback, so that for instance if you deliver an `output' equivalent to raising your hand, you get `feedback' as if your hand had risen. The scientist has put you into a virtual reality, so your virtual hand rises. And, it seems, you would have no way of knowing that this had happened, since to you it would seem just as if a normal life was continuing.

    Descartes's own version of the thought-experiment does not cite brains and vats. In fact, if you think about it, you will see that he does not need to do so. Our beliefs about the brain and its role in generating conscious experience are beliefs about the way the world works. So perhaps they too are the result of the Evil Demon's inputtings! Perhaps the Demon did not need to get his hands (?) dirty messing around in vats. He just inputs experiences in whatever way is made appropriate by the real reality. Brains and nerves themselves belong to the virtual reality.

    This thought-experiment does not cite actual illusions of sense, or actual dreams. It simply sets experience as a whole against a very different and potentially disturbing reality. Notice as well that it is not obviously useful to argue against the Evil Demon hypothesis by citing the coherence and scale of everyday experience. For we do not know of any reason why the Demon could not input experience as coherent as he wishes, and of whatever scale or extent he wishes.

    So how could we possibly rule out the Evil Demon hypothesis? Once it is raised, we seem to be powerless against it.

    Yet, in this sea of doubt, just when things are at their darkest, Descartes finds one certain rock upon which he can perch. `Cogito, ergo sum': I think, therefore I am. (A better translation is `I am thinking, therefore I am'. Descartes's premise is not `I think' in the sense of `I ski', which can be true even if you are not at the moment skiing. It is supposed to be parallel to `I am skiing'.)

    Even if it is a virtual reality that I experience, still, it is I who experience it! And, apparently I know that it is I who have these experiences or thoughts (for Descartes, `thinking' includes `experiencing').

    Why does this certainty remain? Look at it from the Demon's point of view. His project was to deceive me about everything. But it is not logically possible for him to deceive me into thinking that I exist when I do not. The Demon cannot simultaneously make both these things true:

I think that I exist. I am wrong about whether I do.

Because if the first is true, then I exist to do the thinking. Therefore, I must be right about whether I exist. So long as I think that (or even think that I think it), then I exist.

    I can think that I am skiing when I am not, for I may be dreaming, or deluded by the Demon. However, I cannot think that I am thinking when I am not. For in this case (and only this case) the mere fact that I think that I am thinking guarantees that I am thinking. It is itself an example of thinking.


Outside the context of the doubt, the `I' that thinks is a person that can be described in various ways. In my case, I am a middle-aged professor of philosophy, with a certain personality, a history, a network of social relations, a family, and so on. But in the context of the doubt, all this is swept away: part of the virtual reality. So what is the `I' that is left? It seems very shadowy--a pure subject of thought. It might not even have a body! This takes us to the next twist.

    You might try peering into your own mind, as it were, to catch the essential `you'. But, remembering that the `you' (or the `I' from your point of view) is here separated from normal marks of identity (your position in space, your body, your social relations, your history), it seems there is nothing to catch . You can become aware of your own experiences, but never, it seems, aware of the `I' that is the subject of those experiences. Or you can try to imagine the self, to frame a picture of it, as it were. But as Descartes remarks, imagination seems good at framing pictures of things that have shape and size, and are found in space (`extended things'). The self that remains as the rock in the seas of doubt may not be an extended thing. For we can be certain of it when we are still uncertain about extended things, since we are taking seriously the possibility of the Evil Demon.

    One reconstruction of this point of the argument presents Descartes thinking like this:

I cannot doubt that I exist. I can doubt whether things extended in space (`bodies') exist. Therefore, I am not a body.

In a nutshell, souls are certain, bodies are doubtful, so the soul is distinct from the body. If this is Descartes's argument, then it is superficially plausible, but can be seen to be invalid. For consider the parallel:

I cannot doubt that I am here in the room. I can doubt whether a person who will get bad news tomorrow is in the room. Therefore , I am not a person who will get bad news tomorrow.

A nice proof with a welcome result! The fallacy is often called the `masked man fallacy': I know who my father is; I do not know who the masked man is; so , my father is not the masked man.

    I myself doubt if Descartes committed this fallacy, at least in this Meditation . At this point he is more concerned with the way in which we know anything about souls and bodies. He is not concerned to prove that they are distinct, but more concerned to show that knowledge of the self is not dependent upon knowledge of bodies. Because the one can be certain, even when the other is not. Nevertheless, what are we left really knowing about the self?

    In the following century the German philosopher Georg Christoph Lichtenberg (1742-99) remarked: `We should say, "it thinks" just as we say, "it thunders". Even to say "cogito" is too much, if we translate it with "I think".' (Lichtenberg liked pithy aphorisms, and was an important influence on a yet later figure, Friedrich Nietzsche [1844-1900].)

    The idea is that the apparent reference to an `I' as a `thing' or subject of thought is itself an illusion. There is no `it' that thunders: we could say instead just that thunder is going on. Similarly Lichtenberg is suggesting, at least in the context of the doubt, that Descartes is not entitled to an `I' that is thinking. All he can properly claim is that `there is a thought going on'.

    This seems a very bizarre claim. For surely there cannot be a thought without someone thinking it? You cannot have thoughts floating round a room waiting, as it were, for someone to catch them, any more than you can have dents floating around waiting to latch onto a surface to be dented. We return to this in Chapter 4. But then why isn't Lichtenberg right? If Descartes cannot confront a self that is doing the thinking, cannot experience it, cannot imagine it, then why is he entitled to any kind of certainty that it exists? Indeed, what can it mean to say that it exists?

    Descartes adroitly puts this problem to one side, by raising a parallel difficulty about `things which people commonly think they understand most distinctly of all'--ordinary bodies, or things met with in space. This is what was aimed at by the ball of wax example. Here is a possible reconstruction of the argument:

At a particular time, my senses inform me of a shape, colour, hardness, taste that belong to the wax. But at another time my senses inform me of a different shape etc. belonging to the wax. My senses show me nothing but these diverse qualities (which we can call `sensory qualities', since our senses take them in). I nevertheless make a judgement of identity: it is the same piece of wax on the earlier and the later occasion. So, it is the nature of the ball of wax that it can possess different sensory qualities at different times. So, to understand what the wax is I must use my understanding, not my senses.

If this is a good reconstruction, we should notice that Descartes is not denying that it is by means of the senses that I know that the wax is there in the first place (assuming we have got rid of the Evil Demon, and are back to trusting our senses). In fact, he goes on to say as much. Rather, he is suggesting that the senses are like messengers that deliver information that needs interpreting . And this interpretation, which is here a question of identifying the one object amongst the many successive appearances, is the work of the understanding. It is a matter of employing principles of classification, or categories, whose credentials we can also investigate.

    So, all we can understand by the wax is that it is some elusive `thing' that can take on different bodily properties, such as shape, size, colour, taste. And we understand by the self, the `I', just some equally elusive `thing' that at different times thinks different thoughts. So maybe the self should not be regarded as especially mysterious, compared with everyday things like the ball of wax. Perhaps selves are no harder to understand than bodies, and we only think otherwise because of some kind of prejudice. We return to the wax in Chapter 7.


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