2. Reasons to Doubt in the First Meditation

Let us briefly review the sequence of doubts that begin the Meditations. When Descartes looks for reasons to doubt the senses, he first notes that the senses sometimes deceive, and that those who deceive even once are not worthy of trust. But though they sometimes deceive us about things which are very small or very distant, we would surely be insane, he says, to doubt the evidence of our senses when we see our hands in front of our faces. Then he reflects that dream experience can seem as evident; dreams may trick us into believing that we are sitting by the fire when we are asleep in bed. Finally, he suggests that an omnipotent God could have brought it about that there is no earth, no sky, no extended thing, no shape, no size, no place, while ensuring that these things appear to us to exist just as they do now.Footnote ¹⁷

Does Descartes seriously expect us to doubt our senses on the basis of these considerations? He describes his conclusion that all his former beliefs are subject to doubt as ‘based on powerful and well thought-out reasons’, and continues:

Descartes here presents suspension of belief as the rational response to his sceptical arguments. Surely Hume and Reid are right to regard it as psychologically impossible, not to speak of irrational, not to believe our senses on these grounds.

Maybe so, but is this what Descartes intended? We must read him carefully. The resolution expressed in (1) is conditional: if he wants to discover any certainty (the French translation adds, ‘in the sciences’), then he must withhold assent from his former beliefs. This suggests that suspension of belief is the rational response to his sceptical arguments under certain conditions, the conditions depicted in the opening paragraphs of the Meditations. Call the person in these conditions ‘the meditator’. In his guise as meditator, Descartes earlier says:

For the meditator, reason dictates that assent should be withheld from beliefs that are subject to any doubt at all. Consequently, suspension of belief is the meditator's rational response to the sceptical arguments. But why is it rational for the meditator to withhold assent from beliefs that are in any sense dubitable, as (2) claims? Notice that the meditator says ‘Reason now leads me to think…’. This suggests, again, that there is something about the meditator's specific conditions that makes it rational to withhold assent from anything dubitable. What are these conditions? The Meditations begins thus:

The later reference to certainty in (1) presumably alludes to this aim of establishing something stable and lasting in the sciences. Passage (3) tells us that stable certainties can be established in the sciences only if we demolish our existing beliefs and start afresh. This demolition is necessary, Descartes says, because our beliefs constitute a doubtful structure based on falsehoods accepted in our infancy. Taken together, passages (2) and (3) tell us that if we seek to demolish a belief structure based on falsehoods accepted in childhood in order to establish stable certainties in the sciences, then it is rational for us to withhold assent from beliefs about which any doubt can be raised. Only in the context of this project of demolition and reconstruction, then, does Descartes claim that the meditator should withhold assent from the senses on the basis of his sceptical arguments.

What are the implications of this for the objection that Cartesian doubt about the senses is both impossible and fruitless? Firstly, it implies that the sceptical arguments are not expected to induce suspension of belief all on their own, as it were. The role of the sceptical arguments is simply to show that our beliefs are ‘in some sense doubtful’, as Descartes puts it. It is only in the context of the resolution to demolish our existing beliefs and start afresh that it is rational to suspend belief in whatever is in some sense doubtful. Secondly, it means that the feasibility and value of suspension of belief in the senses depends on the feasibility and value of the project of demolishing our existing beliefs in order to establish something lasting in the sciences. What reason does Descartes give to persuade us that this project of demolition and reconstruction is necessary?

At first sight, the motivation Descartes offers for the project seems slender. He says that he was struck by the large number of falsehoods he had accepted as true in his childhood. Presumably we can all think of some falsehoods we accepted as true in childhood; perhaps, as children, we believed that Father Christmas brought us presents, or that monsters lived under the bed, or that babies are delivered by storks, or some such. But the fact that we now recognise these falsehoods as such means that we no longer accept them, so it is hard to see how they could render other beliefs we have dubious. Presumably we are all modest enough to accept that we have some unrecognised false beliefs, some of which may well have been acquired in childhood. But this commonplace observation hardly seems to necessitate what Descartes describes as the ‘enormous task’ of demolishing all our beliefs and starting again from the beginning. If some of our beliefs are false, why not identify and correct them piecemeal, instead of attempting to reject all our opinions at once?

The fact that the rationale for the project of demolition and reconstruction seems so slight fuels the suspicion that Descartes has another agenda, such as a particular conception of knowledge or of enquiry, or a preoccupation with indubitability. Descartes does have an agenda that cannot be revealed to the reader at this initial stage, if only in the sense that he knows what the outcome of the project will be, while the reader does not. But this point is compatible with many different views of what that agenda is, of what Descartes aims to achieve through the use of doubt. I suggest that we should take Descartes at his word when he says that the reason we should demolish and rebuild our beliefs is that they are founded on falsehoods accepted in childhood. On this more literal reading of the aim and motivation for the project of doubt, it is precisely because we are subject to these founding falsehoods that cognitive reform is needed.Footnote ²¹ Let us see what can be said for this for this more literal reading of Descartes's agenda.

3. The Consequences of the Errors of Childhood

The ill-formed, ill-founded character of our early beliefs and the consequent necessity of starting afresh is a frequent theme in Descartes's work. The earlier Discourse compares our beliefs to an unplanned city that has grown up through the haphazard addition of buildings, the unfinished Search After Truth compares them to a picture badly drawn by a young apprentice, and the Seventh Replies compares them to a barrel of sound apples contaminated by rotten ones. In all three cases the defective character of our beliefs is connected to their childhood origin. Descartes writes:

Descartes uses these comparisons to recommend the demolition of the city, the erasure of the drawing, the emptying of the barrel; the city is to be rebuilt according to a plan, the picture redrawn by the master artist, the barrel refilled with sound apples. Similarly, the opinions acquired since childhood should be cleared away, so that they can be replaced with better ones:

The architectural metaphors used in the Discourse and Search indicate the instability of childhood opinions as a foundation for our beliefs. The passages from the Search and the Seventh Replies emphasise the magnitude of the falsity to be found in opinions formed in childhood. The Discourse, Search and Principles link the falsity of these beliefs to the fact that the intellect or reason is not fully developed in childhood; the Search and Principles also implicate the senses in these errors. The description of our predicament in the Search is particularly striking:

Here the faults in the image sketched by the apprentice are so extensive and so fundamental that it is necessary for the master to erase it and begin again; the picture cannot be corrected piecemeal. The message of the simile is that the errors in the opinions acquired in childhood via our senses, instincts and teachers are so extensive and so fundamental that the intellect, the master, cannot correct them one by one. This message is most explicit in the opening words of the later Principles:

This passage also mentions a further problem: the opinions acquired in childhood are not just false, they are also obstacles to the knowledge of the truth.

It is clear from these texts that the project of demolishing and reconstructing our opinions is not motivated simply by the banal observation that we acquire the occasional false belief in childhood. In Descartes's view, the mistakes we make in childhood are so fundamental and so pervasive that piecemeal correction is hopeless; that is why we must ‘demolish everything completely and start again right from the foundations’.Footnote ³⁰ When he begins the Meditations by speaking of the ‘large number’ of falsehoods accepted in childhood, and the ‘highly dubious’ character of the beliefs based on them, he is perfectly sincere.

4. The Need to Doubt the Senses

What is the nature of these fundamental childhood errors? When Descartes sets to work to undermine the edifice of belief, he targets the senses: ‘whatever I have up till now accepted as most true I have acquired by or through the senses’.Footnote ³¹ The implication is that the many basic falsehoods taken as true in childhood are acquired through reliance on the senses. That this is his considered view is plain from Descartes's explicit descriptions of our early cognitive development, as well as his frequent references to the prejudices of the senses.Footnote ³² The later Principles states that ‘the chief cause of error arises from the prejudices of childhood’.Footnote ³³ Our infant reliance on the senses imbued our minds with ‘a thousand prejudices’; and in later childhood, ‘forgetting that they were adopted without sufficient examination’, we regarded these prejudices as ‘known by the senses or implanted by nature, and accepted them as utterly true and evident’.Footnote ³⁴

How do these prejudices ‘keep us from knowledge of the truth’, as Descartes claims they do? He explains in the Second Replies that the reason it is difficult for us to perceive the primary notions of metaphysics clearly and distinctly is that they conflict with ‘many prejudices derived from the senses which we have got into the habit of holding from our earliest years’.Footnote ³⁵ He writes in the earlier Discourse that

As this passage shows, Descartes believes that our childhood reliance on the senses entrenches a habit of thinking in terms of what can be sensed. The soul is thought of, if it is thought of at all, as a kind of attenuated body, a wind or ether permeating the limbs.Footnote ³⁷ Things that do not affect the senses, such as God and the soul, are regarded as difficult to know. Conversely, bodies are regarded as easy to know, since they are assumed to resemble our sensory perceptions completely.Footnote ³⁸ For example, distant stars are taken to be small, because that is how they appear to our senses; space where we sense nothing is taken to contain nothing corporeal; bodies are taken to possess heat, colour and other sensible qualities wholly resembling our sensory perceptions.Footnote ³⁹

In contrast to what he regards as the widespread conviction that it is difficult to know God and the soul, Descartes believes that our own minds and God are ‘the most certain and evident of all possible objects of knowledge for the human intellect’. That, he says, is the one thing he set himself to prove in the Meditations.Footnote ⁴⁰ This remark testifies to the importance Descartes attaches to overcoming the prejudices of the senses and learning to appreciate ‘the certainty that belongs to metaphysical things’ such as God and the soul.Footnote ⁴¹ Thanks to the continuing effect of the habitual prejudices of the senses, ‘only those who really concentrate and meditate, and withdraw their minds from corporeal things, so far as is possible, will achieve perfect knowledge’ of metaphysical things.Footnote ⁴² The ‘greatest benefit’ of the First Meditation doubt, Descartes says, is precisely that it both frees our minds from prejudices, and provides a way to draw the mind away from the senses.Footnote ⁴³

In effect, the Meditations attempts to correct the effects of the process that occurred in childhood, when our minds were stocked with beliefs acquired through reliance on the senses, and the intellect exercised little or no critical scrutiny. Hence Descartes writes,

These long-standing opinions based on the senses are to be eradicated, and our minds are to be re-stocked with opinions subjected to the scrutiny of the intellect and based on firm reasoning. If this is Descartes's plan, it is clear that it can proceed only if we really do renounce our old opinions and cease to trust our senses, so far as we can. So the questions raised by Hume and Reid press with particular force. How can we do this if we could not doubt our senses without falling into danger? How can we do this if we are psychologically incapable of doubting our senses?

Precisely because he is so insistent that his readers should genuinely withdraw their minds from their senses, Descartes is sensitive to these questions of practicality. He stresses that the meditator should have ‘a clear stretch of free time’Footnote ⁴⁵, and that the task of meditation ‘does not involve action but merely the acquisition of knowledge’.Footnote ⁴⁶ If the meditator is sitting quietly, engaged only in meditation, the danger of walking into posts is minimal. But of course there is no such danger if it is psychologically impossible for us not to trust our senses. What is Descartes's response to this charge?

Descartes holds that trust in the senses is both habitual and natural for us. It is natural because we have, he believes, a strong natural propensity to believe that we perceive material bodies when we sense. It is habitual because we are in the habit of believing that the senses are the source of certainty and truth. Having decided in the First Meditation that he must withhold assent from his existing opinions, he finds that these habitual opinions ‘keep coming back, and despite my wishes, they capture my belief, which is as it were bound over to them as the result of long occupation and the law of custom’.Footnote ⁴⁷ The existence of these natural and habitual tendencies to belief means that a special measure is needed to enable the meditator to withdraw the mind from the senses and suspend belief in the existence of bodies, so far as possible.Footnote ⁴⁸ The measure Descartes uses is the pretence of falsity. He resolves to deceive himself by ‘pretending for a time that these former opinions are utterly false and imaginary’; and he resolves to do this until ‘the weight of prejudice is counter-balanced and the distorting influence of habit no longer prevents my judgement from perceiving things correctly’.Footnote ⁴⁹ As he says here, the pretence of falsity is needed to counteract the effect of the prejudices ingrained since childhood, the habits that distort our judgement and prevent us from perceiving clearly and correctly. Although it is a pretence, it serves the purpose of counteracting our natural and habitual tendencies towards belief in the sensible world. Before we examine how the pretence of falsity is put to use, it will be useful to clarify the character of the fundamental error of childhood.

5. The Nature of the Founding Error

Is our fundamental error an error of the senses, or an error of judgement? On the one hand, when Descartes sets out to undermine the foundations of our existing opinions in the First Meditations, he targets the senses, saying that ‘whatever I had accepted as most true I had accepted by or through the senses’.Footnote ⁵⁰ And we have already seen that he attributes our childhood errors to a preoccupation with the senses. On the other, Descartes invokes the pretence of falsity to counteract prejudices or pre-judgements, and to correct the effect of habits that distort our judgement.

Descartes finally identifies our fundamental error regarding the senses in the Sixth Meditation. It is that of misusing sensory perceptions by treating them as reliable guides for immediate judgements about the essences of external bodies, without waiting for the intellect to examine the matter.Footnote ⁵¹ In doing this, he says, we habitually pervert the order of nature.Footnote ⁵² The proper purpose of our sensory perceptions is to inform the mind of what is beneficial or harmful for the mind-body composite, the human being. When we use them as touchstones for immediate judgements about the essences of the external bodies we sense, we use them for an unnatural and improper purpose.

It is clear from this diagnosis that the founding error is an error of judgement, rather than of the senses proper. The character of the error fits Descartes's description of the predicament of the human mind in infancy. Our earliest judgements, he believes, are governed by our desire to survive. As a result, in childhood ‘the mind judged everything in terms of its utility to the body in which it was immersed’.Footnote ⁵³ Since our capacity for sensory perception is given to us by Nature as a guide to what is beneficial and harmful to us as embodied creatures, it is not surprising that the infant should rely on sensory perceptions for survival. As Descartes explains in the Sixth Replies,

The founding error becomes entrenched when the confused judgements made in childhood become habitual, instead of being revised in later life.

Descartes's claim that we pervert or overturn the order of nature might be taken to mean that we allow the senses to usurp the place of the intellect. But that would suggest that the senses and the intellect compete for the control of judgement, and that is not how he views the matter. For Descartes, the senses and the intellect are faculties of perception; they do not make judgements. Judgement occurs only when we affirm or deny the content of a perception by an act of will. Our errors of judgement stem from our misuse of our free will (as it must do, given that the author of our nature is not responsible for them). We use our wills incorrectly whenever we affirm something without perceiving its truth with sufficient clarity and distinctness; and this is what we do habitually when we draw conclusions about the nature of external bodies from sensory perceptions without adequate intellectual examination. Such judgements are erroneous in Descartes's specific sense of the term: they involve the incorrect use of free will that is, for him, the essence of judgement error.Footnote ⁵⁵

Mistaking the epistemic role of the senses, we treat sensory perceptions as the source of certainty. The founding error, then, is an error of judgement that becomes habitual. In particular, we habitually judge that external things wholly resemble our sensory perceptions. Worse still, we fail to recognize our responsibility for these judgements; we regard our habitual view of the world as implanted by nature or known by the senses, as he puts it in the Principles.Footnote ⁵⁶ This mistake is reinforced by the fact that we fail to recognize the role of judgement in what we call ‘sensing’. The senses do not make judgements, but the final stages of what we call sensing are the product of judgement, the work of the intellect and will. There is no falsity in the sensory perceptions of external objects that occur in our minds when our sense organs are stimulated.Footnote ⁵⁷ Descartes does describe these perceptions as materially false, but this simply means that they provide material for false judgements.Footnote ⁵⁸ Because these ideas are obscure and confused, we are liable to misudge their objects.Footnote ⁵⁹ In particular, we are liable to judge that they represent qualities in objects which they wholly resemble, as happens when we judge that heat in a body is something wholly resembling the idea of heat that is in us.Footnote ⁶⁰ Sensory perceptions of heat are given to us by nature to inform us of the potential of other bodies to help or harm our own, and as such they are sufficiently clear and distinct.Footnote ⁶¹ Sensory perceptions also carry information about the essential natures of these bodies, but in an obscure form.Footnote ⁶² That is why careful thought is needed if we are to make true judgements about the corporeal world on the basis of such perceptions. In Descartes's view, we are solely responsible for the mistakes we make when we judge without such careful thought; the sensory ideas themselves are not the source of our errors.

This point is worth stressing because it is so often missed. It is easy to miss, because Descartes himself obscures it by his talk of the errors and prejudices of the senses. When he speaks in this way, Descartes is speaking colloquially, attributing to the senses what is actually the result of judgement.Footnote ⁶³ His considered view is that we do make fundamental errors because of our reliance on the senses, but these errors are not due to our reliance on a faculty that is by nature unreliable, erroneous or otherwise faulty. Our benevolent creator would not, indeed could not give us such a faculty. Instead, the errors are due to our misuse of a faculty of sensation that is perfectly in order, and indeed testifies to the power and goodness of God.Footnote ⁶⁴ We err when we misuse sensory perceptions by assigning them a role for which nature (i.e. God) did not intend them.

6. Correcting the Founding Error

Let us now begin to map out the way in which the Meditations uses doubt about the senses to correct the founding error. As we saw, Descartes directs us to pretend that our long-standing opinions are false, that our senses delude us, to ensure that we do not slip back into our errors. The pretence of falsity is put into effect using the device of the evil demon. We are to suppose that we are being deceived by a demon of the utmost power and cunning, who not only supplies us with delusory experience but also deludes us about the very existence of bodies. This supposition is intended to disrupt our habitual trust in the senses and to draw our minds away from their preoccupation with sensible things.

Pursuing this supposition, Descartes begins the Second Meditation by supposing that everything he sees is spurious (falsa), that his memory lies, that he has no senses, that body, shape, extension and place are chimeras.Footnote ⁶⁵ The first fruit of this rejection of the sensible is a conception of the self as ‘a mind, or intelligence, or intellect, or reason – words whose meaning I have been ignorant of until now’.Footnote ⁶⁶ This grasp of the self as a thinking thing does not depend on the grasp of anything corporeal; in fact, it is arrived at by supposing the non-existence of anything corporeal. This being so, Descartes argues, the mind must be ‘most carefully diverted’ from sensory images of corporeal things ‘if it is to perceive its own nature as distinctly as possible’.Footnote ⁶⁷

Despite having been introduced to this intellectual grasp of the self as a mind, the meditator ‘cannot stop’ thinking that corporeal things, which can be sensed and imagined, are known more distinctly than the mind, which cannot.Footnote ⁶⁸ Descartes confronts this childhood prejudice directly through the examination of the piece of wax. The essential nature of the wax is grasped not by the senses, which perceive only its outward forms, nor by the imagination, which can form only a limited number of images, but by the intellect, when we understand that the wax is a body capable of being extended in an infinity of different ways. Even what we call ‘seeing with our eyes’ involves an act of judgement, Descartes argues. We judge that the wax is there before us when we perceive its colour and shape, just as we judge that there are men in the square below us when we see hats and coats. Hence we not only perceive what the wax is using the intellect, by conceiving of it as an extended body; we also perceive the wax itself using the intellect when we do what we ordinarily call ‘sensing’ it.

This claim that what we call ‘sensing’ involves an intellectual act is elaborated in his discussion of the three grades or stages of sensing in the Sixth Replies. The first stage consists of physical motions in the bodily organs, the second of the immediate mental effects of these, ‘including perceptions of pain, pleasure, thirst, hunger, colours, sound, taste, smell heat, cold and the like’ (AT VII 437, CSM II 294). Sensing proper ends with these. The third stage includes ‘all the judgements about things outside us which we have been accustomed to make from our earliest years’ (AT VII 437, CSM II 295); but ‘when from our earliest years we have made judgements, or even rational inferences, about the things that affect our senses’, we do not distinguish these judgements from simple sense-perception. Descartes writes:

Thus we refer these judgements to the senses because they are so habitual that they have become, in effect, an automatic part of the process set in train by the stimulation of our sense organs.

The realisation that much of what we call sensing is in fact the work of the intellect is of key importance for Descartes's project of challenging the ‘prejudices of the senses’. It marks the meditator's first step on the path to exposing the founding error. The second step is taken in the Third Meditation, when Descartes identifies

Why, he asks, do we believe that external things are wholly similar to our sensory ideas? (Notice that the accent is on the resemblance claim, rather than the existence claim.) Firstly, nature has apparently taught us to think this; that is, we have a spontaneous impulse to believe it. But our natural impulses have led us astray in the past, so this is not a good enough reason. Secondly, we think that our sensory ideas come from something outside us, because their occurrence is not under our control; and the most obvious judgement for us to make is that these external things transmit their likenesses to us. But this is not a good enough reason either. These ideas might come from a source within us, as they do when we are dreaming; and even if they come from external things, that does not entail that they must resemble them. Here Descartes points out that we have two incompatible ideas of the sun. One, derived from what we call sensing, represents it as small; the other, derived from astronomical observation and reasoning, represents it as many times larger than the Earth. The sun cannot resemble both ideas, and in this case we judge that the first idea is the one it least resembles.Footnote ⁷⁰

Descartes concludes that it is ‘not reliable judgement but merely some blind impulse’ that has made us believe up till now that there are external things which transmit their likenesses to us through the senses.Footnote ⁷¹ As we have seen, the belief that external bodies wholly resemble our sensory perceptions is one of the most entrenched prejudices of childhood (as well as a cornerstone of Scholastic Aristotelian epistemology). This habitual belief now appears far more dubious than it did after the arguments of First Meditation. There habitual beliefs were still regarded as being highly probable opinions, ones it is much more reasonable to believe than deny.Footnote ⁷² By this point in the meditator's progress, this habitual belief seems to be without justification.

The belief in the existence of external bodies wholly resembling our sensory perceptions is finally reassessed in Sixth Meditation, in the light of the knowledge of own nature and its creator that has been gained through meditating. Descartes's reasoned proof of the existence of body appeals to the fact that God has given us a ‘great propensity’ to believe that our sensory perceptions are caused by material things, and no faculty for recognizing any other source. The impulse to believe that sensory ideas are caused by external bodies is thus legitimated as a natural propensity bestowed by a veracious creator. Now that we know that our creator is not a deceiver, we can say that

Descartes claims that our God-given nature teaches us that we have bodies to which we are united, and that our bodies are surrounded by other bodies that vary in ways corresponding to the variation in our sensory perceptions.Footnote ⁷⁴ But the impulse to believe that external bodies wholly resemble sensory ideas is not legitimated as a teaching of nature. Descartes writes:

The beliefs listed here are childhood prejudices, beliefs acquired through a habit of making judgements without due consideration that dates back to our earliest years. Since they all reflect the assumption that external bodies wholly resemble our sensory perceptions, that assumption too is a prejudice of childhood. The impulse to believe that external things resemble sensory ideas is revealed as an acquired tendency masquerading as a teaching of nature.

Teachings of nature and childhood habits are easily confused, since long-standing habits are so familiar that they seem natural to us. But their provenance, and hence their epistemic status, is completely different. Teachings of nature come from a God who cannot deceive, so they are guaranteed to contain some truth.Footnote ⁷⁶ Habits of judgement acquired in childhood are most likely to be false. In childhood, as we saw, we are reliant on sensory perceptions for survival, and we come to treat them as infallible guides to truth, a role they were never intended to play. Descartes explains this in an important discussion in which he clarifies what he means by a teaching of nature. Our nature as embodied minds teaches us to avoid external bodies that cause painful sensations, since these are signs of potential harm, and to seek out ones that cause pleasant sensations, since these are signs of potential benefit. It is here that he says that the proper purpose of the sensory perceptions given to us by nature is simply to inform the mind of what is beneficial or harmful to the mind-body composite. But our nature as composites of mind and body

This is a crucial passage. Descartes claims that knowledge of the truth about external bodies belongs to the mind alone, and that is why intellectual examination is required before we make judgements about such things on the basis of sensory perceptions. Of course we made such judgements without intellectual examination in childhood, before we had full use of our reason. But we are at fault because we have continued to make them ever since, even though we now have the capacity to correct them.Footnote ⁷⁸ Through our failure to correct them, we are

We misuse sensory perceptions when we make them the basis for precipitate judgements about external things without waiting for the intellect to examine the matter.Footnote ⁸⁰ This is the founding error of childhood, which we are now in a position to correct.

This is the final step on the path to correcting the prejudices of the senses. It makes essential use of the lesson learned at the first step, in the Second Meditation, when the meditator discovered that bodies such as the wax are known not by the senses but by the mind alone. This lesson is applied when the meditator reasons that knowledge of the truth about external bodies belongs to the mind alone, not the mind-body composite. Our natures as composites teach us to avoid things that cause pain and seek out what causes pleasure, but it does not teach us to draw conclusions from sensory perceptions about external things ‘without waiting until the intellect has examined the matter’.Footnote ⁸¹ Our tendency to do this is not natural, as we take it to be, but habitual. By nature, knowledge of the truth about external things ‘belongs to the mind alone’, and that is why we must examine and interpret sensory perceptions before we make judgements about the natures of external bodies.Footnote ⁸² Our failure to do this is the source of the founding error that perverts our nature.

7. The Role of Doubt About the Senses

What role does doubt about the senses play in the process of correcting the founding error? One might think that it operates only at the outset, that it simply helps to wipe the slate clean, to free our minds from our old beliefs or prejudices, so that the process of reconstruction can begin. But such an interpretation would obscure the process of active doubting in which Descartes wants us to engage as the Meditations progresses. As we have seen, Descartes states in the Synopsis that the greatest value of the First Meditation doubt is that it frees our minds from prejudices and lays down the easiest route by which the mind may be drawn away from the senses.Footnote ⁸³ But he describes the actual withdrawal of the mind from the senses as occurring in the Second Meditation, in which the mind uses the freedom it has gained to suppose the non-existence of things perceived through the senses, and thereby becomes aware of its own nature for the first time.Footnote ⁸⁴ He claims in the Second Replies that although many writers had said that the mind must be drawn away from the senses in order to understand metaphysical matters, no one had shown how this could be done. He, Descartes, has provided the correct – and, he claims, unique – method of doing this in the Second Meditation.Footnote ⁸⁵

As we saw, Descartes begins the Second Meditation by supposing that everything he sees is spurious (falsa), that his memory lies, that he has no senses, that body, shape, extension and place are chimeras.Footnote ⁸⁶ The pretence of deception by the demon is invoked several times (AT VII 24–6, CSM II 17–8), reinforcing the thought that sensory images are no more than dreams (AT VII 28, CSM II 19). By disregarding sensory images and denying that anything material exists, we learn to distinguish what belongs to an intellectual nature from what belongs to corporeal things (AT VII 131, CSM II 94).

This direction of mental attention away from sensory perceptions and towards the objects of the understanding is a reversal of the direction it has had since childhood. So it is not surprising that Descartes warns that ‘protracted and repeated study’ of the Second Meditation is required ‘to eradicate the lifelong habit of confusing things related to the intellect with corporeal things, and to replace it with the opposite habit of distinguishing the two’.Footnote ⁸⁷ It takes effort to withdraw attention from sensory images and concentrate the mind on things that cannot be sensed.Footnote ⁸⁸ We have to learn to exercise ‘the intellectual vision which nature gave [us], in the pure form which it attains when freed from the senses; for sensory appearances generally disturb and obscure it to a very great extent.Footnote ⁸⁹

By the start of the Fourth Meditation, the meditator can declare that

The meditator now understands that our own minds and God are ‘the most certain and evident of all possible objects of knowledge for the human intellect’, as Descartes puts it in the Synopsis.Footnote ⁹¹

This realisation corrects one of the prejudices of childhood, the belief that God and the soul are difficult to know because they cannot be sensed. But how does withdrawing the mind from the senses in the Second Meditation enable us to correct our erroneous beliefs about things that can be sensed? At the start of the Third Meditation, the meditator realises that the habitual judgement that there are things outside us wholly resembling our sensory ideas is not based on clear perception, and may be false. What puts us in a position to realise this? The realization follows the acknowledgement that we ‘previously accepted as wholly certain and evident many things which [we] afterwards realized were doubtful’, namely, the earth, sky, stars, and everything that we apprehended with the senses.Footnote ⁹² Presumably these things were realized to be doubtful in the First Meditation. But now the meditator is able to isolate why it is that these things we apprehend through the senses are doubtful. That we have sensory ideas of such things is not in doubt. But the claim that there are external things that wholly resemble our sensory ideas of earth, sky, stars and so on is now recognized as being doubtful because we do not clearly and distinctly perceive that it is true. If we were as certain of this as we are that we are thinking things, we would not be able to doubt it; or, rather, we would be able to doubt it only by doubting the truth of clear and distinct perceptions.

Withdrawal from the senses, as practiced in the Second Meditation, contributes to this discovery in two ways. Firstly, withdrawal from the senses enables us to learn what clear and distinct perception is like. Through discounting sensory images and denying that any body exists, we are able to form ‘a concept of the soul which is as clear as possible and is also quite distinct from any concept of body’.Footnote ⁹³ We are also able to form a clear and distinct intellectual conception of the piece of wax as an extended thing. Secondly, withdrawal from the senses enables us to understand the limitations of the senses, through the examination of the piece of wax. It reveals that what we call ‘sensing’ a particular body involves intellectual judgement, and it reveals that the senses grasp the outward forms of extended things. We judge that the wax is there from the colour and shape that we perceive; knowledge of the wax comes from the scrutiny of the mind alone, not from what the eye sees.Footnote ⁹⁴ But this means that the judgements that the wax is there, and that the wax is thus-and-so, require reasons. If we perceived the existence of the wax as clearly and distinctly as we perceive our own existence, we would be as certain of the former as we are of the latter. However, our claims about the existence of external bodies are not based on clear perception, so we are able to doubt their existence despite our natural propensity to affirm it.

The Second Meditation thus plays a key role in exposing the prejudices of the ‘senses’ and revealing the standard of clear intellectual perception to which they are to be compared. This fact helps to explain an aspect of Descartes's procedure which might otherwise be puzzling. Descartes believes that our assumption that there are bodies resembling our sensory perceptions is a prejudice, a judgement made without clear rational support. So why does he not launch straight into the critique of the grounds for this judgement at the start of the Meditations? Why postpone it until the Third Meditation?

The judgement that we perceive material things through the senses is one that Descartes thinks we have a strong natural propensity to make, so it is not easy for us to withhold assent from it. That is why we need the arguments of the First Meditation to give us reason to withhold assent from it, and the pretence of deception by the demon to enforce the withholding of assent. The belief that external things wholly resemble sensory ideas is not natural, but it is strongly fixed in our minds by habit, so similar measures are needed to loosen our allegiance to it. Our attachment to the senses is so deep-rooted that we are unable to achieve clear intellectual perception until it is loosened; and we need to experience the certainty that attaches to clear and distinct perception in order to realize that the belief is not genuinely certain, but only seems certain because of its familiarity.Footnote ⁹⁵

So, the First Meditation doubt about the senses, carried forward by the pretence of deception, introduces the meditator to clear intellectual perception in the Second Meditation. This prepares the way for the Third Meditation critique, which introduces deeper and more theoretically significant reservations about the senses than were mooted in the First Meditation. The Third Meditation critique introduces worries about the reliability of teachings of nature, as distinct from worries about clear and distinct perceptions. Since our natural impulses have lead us astray when choosing the good, it seems that we cannot trust our impulse to believe that there are bodies outside us that resemble our sensory perceptions. This worry is finally resolved in the Sixth Meditation, as we have seen. To resolve it we need to know not only that our nature is the gift of a non-deceiving God, but also which impulses derive from that nature and which are due to habit. The impulse to believe that we perceive material things through our senses is natural, and therefore trustworthy. The impulse to believe that those material things wholly resemble our sensory perception derives from a habit of misusing sensory perceptions as guides to the essential natures of external bodies. It is the intellect, not the senses, that grasps the truth about the bodies we perceive, as we learned in the Second Meditation; and we should not make judgements about the bodies we perceive without proper intellectual examination. Here, finally, the meditator is in a position to expose the founding error of childhood, and to correct the habits of bad judgement that perpetuate it.

8. Responding to Hume and Reid

Hume and Reid charge that Cartesian doubt, particularly doubt about the senses, is so unnatural as to be impossible; and they charge that if it could somehow be achieved, it would be of no benefit. Descartes agrees that it is natural for us to believe that we perceive material things when we sense; that is something our nature teaches us. But he also believes that much of what we think we perceive through the senses is simply the result of habits of judgement. If we seek firmer foundations for the sciences than the prejudices of childhood, we must suspend these natural and habitual tendencies to judgement by pretending that we are deceived by an evil demon. By reversing our long-standing preoccupation with sensible things, this process enables us not only to achieve clear intellectual perception, but also to understand our own natures. In particular, it enables us to expose and correct our erroneous beliefs about the purpose of the senses.

In a sense, then, Hume and Reid are right. They are right that the Cartesian meditator does not doubt the existence of the external world in everyday contexts, since the doubt is practiced only during meditation. The withholding of assent is an artificial exercise, pursued through the pretence of falsity. But Hume and Reid are wrong to claim that Descartes is hypocritical or disingenuous in enjoining us to doubt. The Meditations is a manual for cognitive reform, designed for practical use. If the work is to have the psychological effects Descartes wants to achieve, if his readers are to genuinely reform their ways of thinking, they must genuinely withdraw their minds from the senses and treat their old opinions as false. Nothing less will serve to reverse the bad habits of a lifetime and restore us to our true nature as cognitive agents. Moreover, it is precisely because so much of our thinking is grounded in habit rather than nature that it is possible for us to change it. This marks one of Descartes's most fundamental disagreeements with Hume. For Hume, habit is a manifestation of nature; our most basic beliefs, such as our belief in causal connections, are acquired through the influence of habit on the imagination. For Descartes, nature and habit are in conflict. Our habit of reliance on sensory images obscures the natural light of intellectual perception and leads us to confuse habits of bad judgement with genuine teachings of nature.

If the interpretation of the Meditations sketched here is along the right lines, there is one final challenge that should be addressed. If the errors we make in childhood are as numerous and as pervasive as Descartes claims, how is it that they have so little practical impact on us? Without the corrective exercise of the Meditations, Descartes believes that most people live and die without ever achieving a distinct perception.Footnote ⁹⁶ But most people are not noticeably disadvantaged by this; they still manage to live successful lives. How can this be so? And, if it is so, what advantage could we expect to gain from the arduous task of reversing long-standing beliefs through meditation?

Presumably the errors in question have little everyday impact because they are errors in our beliefs about the underlying structure of the world. Not surprisingly, given their natural purpose, sensory perceptions are a good enough guide to the corporeal world to serve in our daily dealings with it. They tell us where neighbouring objects are and enable us to distinguish them from one another. The fact that we have a confused grasp of the nature of God and the soul has little practical impact. Presumably Descartes thinks that even if we find these metaphysical things hard to understand, we can still know them well enough to do our duty and hope for salvation. Why, then, is it so important for us to correct these errors? Descartes has, I think, at least two answers to this question. Firstly, if we seek to understand the hidden structure of the corporeal world, if we want to understand it well enough to create new technologies in mechanics or in medicine, we must correct our fundamental childhood misapprehensions. In this way, the correction of these errors is necessary for practical advances. Secondly, we will not understand the truth about our own natures and our relationship to God and the corporeal world unless we correct these fundamental mistakes. We will not achieve the clear intellectual perception that is God's gift to the human mind until we correct the habits of thought that block our way. For both these reasons, we cannot set the sciences on a firm foundation until we correct these habitual errors. For Descartes, the aim of the seemingly artificial process of Cartesian doubt is to reverse the distortions of habit and to show us how to use our faculties as nature intended.