\documentclass[12 pt, oneside]{article}   	% use ''amsart'' instead of ''article'' for AMSLaTeX format
\usepackage{geometry}                		% See geometry.pdf to learn the layout options. There are lots.
\geometry{letterpaper}                   		% ... or a4paper or a5paper or ... 
%\geometry{landscape}                		% Activate for rotated page geometry
%\usepackage[parfill]{parskip}    		% Activate to begin paragraphs with an empty line rather than an indent
\usepackage{graphicx}				% Use pdf, png, jpg, or eps§ with pdflatex; use eps in DVI mode
								% TeX will automatically convert eps --> pdf in pdflatex		

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
 
\usepackage{atkinson}

\setlength{\columnsep}{.3 in}

\usepackage{relsize}

\usepackage[colorlinks, hyperfootnotes=false, urlcolor=blue]{hyperref}


\title{Sixth Meditation\footnote{Translation by \href{http://johnstoniatexts.x10host.com/descartes/descartesmeditationshtml.htm}{Ian Johnston} (brackets indicate clarifications from the French edition of 1647); notes by \href{http://www.trevorpearce.com/}{Trevor Pearce}.}}
\author{René Descartes}
\date{1641}							% Activate to display a given date or no date


\begin{document}
\maketitle

It remains for me to examine whether material things exist. At the moment, I do, in fact, know that they can exist, at least to the extent that they are objects of pure mathematics, since I perceive them clearly and distinctly. For there is no doubt that God is capable of producing everything which I am capable of perceiving in this way, and I have never judged that there is anything he cannot create, except in those cases where there might be a contradiction in my clear perception of it. Moreover, from my faculty of imagination, which I have learned by experience I use when I turn my attention to material substances, it seems to follow that they exist. For when I consider carefully what the imagination is, it seems nothing other than a certain application of my cognitive faculty to an object which is immediately present to it and which therefore exists.

In order to clarify this matter fully, I will first examine the difference between imagination and pure intellection. For example, when I imagine a triangle, not only do I understand that it is a shape composed of three lines, but at the same time I also see those three lines as if they were, so to speak, present to my mind’s eye. This is what I call imagining. However, if I wish to think about a chiliagon, even though I understand that it is a figure consisting of one thousand sides just as well as I understand that a triangle is a figure consisting of three sides, I do not imagine those thousand sides in the same way, nor do I see [them], as it were, in front of me. And although, thanks to my habit of always imagining something whenever I think of a corporeal substance, it may happen that [in thinking of a chiliagon] I create for myself a confused picture of some shape, nevertheless, it is obviously not a chiliagon, because it is no different from the shape I would also picture to myself if I were thinking of a myriagon or of any other figure with many sides. And that shape is no help at all in recognizing those properties which distinguish the chiliagon from other polygons. However, if it is a question of a pentagon, I can certainly understand its shape just as [well as] I can the shape of a chiliagon, without the assistance of my imagination, but, of course, I can also imagine the pentagon by applying my mind’s eye to its five sides and to the area they contain. From this I clearly recognize that, in order to imagine things, I need a certain special mental effort that I do not use to understand them, and this new mental effort reveals clearly the difference between imagination and pure understanding.

Furthermore, I notice that this power of imagining, which exists within me, insofar as it differs from the power of understanding, is not a necessary part of my own essence, that is, of my mind. For even if I did not have it, I would still undoubtedly remain the same person I am now. From this it would seem to follow that my imagination depends upon something different from [my mind]. I understand easily enough that if a certain body exists to which my mind is joined in such a way that whenever my mind so wishes, it can direct itself, so to speak, to examining it, then it would be possible, thanks to this particular body, for me to imagine corporeal things. Thus, the only difference between this mode of thinking and pure understanding would be that the mind, while it is understanding, in some way turns its attention onto itself and considers one of the ideas present in itself, but when it is imagining, it turns its attention to the body and sees something in it which conforms to an idea which it has either conceived by itself or perceived with the senses. I readily understand, I say, that the imagination could be formed in this way, if the body exists, and because no other equally convenient way of explaining it comes to mind, I infer from this that the body probably exists—but only probably—and although I am looking into everything carefully, I still do not yet see how from this distinct idea of corporeal nature which I find in my imagination I can derive any argument which necessarily concludes that anything corporeal exists.

However, I am in the habit of imagining many things apart from the corporeal nature which is the object of study in pure mathematics, such as colours, sounds, smells, pain, and things like that, although not so distinctly. And since I perceive these better with my senses, through which, with the help of my memory, they appear to have reached my imagination, then in order to deal with them in a more appropriate manner, I ought to consider the senses at the same time as well and see whether those things which I perceive by this method of thinking, which I call sensation, will enable me to establish some credible argument to prove the existence of corporeal things.

First of all, I will review in my mind the things that I previously believed to be true, because I perceived them with my senses, along with the reasons for those beliefs. Then I will also assess the reasons why I later called them into doubt. And finally I will consider what I ought to believe about them now.

To begin with, then, I sensed that I had a head, hands, feet, and other limbs making up that body which I looked on as if it were a part of me or perhaps even my totality. I sensed that this body moved around among many other bodies which could affect it in different ways, either agreeably or disagreeably. I judged which ones were agreeable by a certain feeling of pleasure and which ones were disagreeable by a feeling of pain. Apart from pain and pleasure, I also felt inside me sensations of hunger, thirst, and other appetites of this kind, as well as certain physical inclinations towards joy, sadness, anger, and other similar emotions. And outside myself, besides the extension, shapes, and motions of bodies, I also had sensations in them of hardness, heat, and other tactile qualities and, beyond that, of light, colours, smells, tastes, and sounds. From the variety of these, I distinguished sky, land, sea, and other bodies, one after another. And because of the ideas of all those qualities which presented themselves to my thinking and which I kept sensing as merely my own personal and immediate ideas, I reasonably believed that I was perceiving certain objects entirely different from my thinking, that is, bodies from which these ideas proceeded. For experience taught me that these ideas reached me without my consent, so that I was unable to sense any object, even if I wanted to, unless it was present to my organs of sense, and I was unable not to sense it when it was present. And since the ideas I perceived with my senses were much more vivid and expressive and even, in their own way, more distinct than any of those which I myself intentionally and deliberately shaped by meditation or which I noticed impressed on my memory, it did not seem possible that they could have proceeded from myself. Thus, the only conclusion left was that they had come from some other things. Because I had no conception of these objects other than what I derived from those ideas themselves, the only thought my mind could entertain was that [the objects] were similar to [the ideas they produced]. And since I also remembered that earlier I had used my senses rather than my reason and realized that the ideas which I myself formed were not as expressive as those which I perceived with my senses and that most of the former were composed of parts of the latter, I easily convinced myself that I had nothing at all in my intellect which I had not previously had in my senses. I also maintained, not without reason, that this body, which, by some special right, I called my own, belonged to me more than any other object, for I could never separate myself from it, as I could from other [bodies], I felt every appetite and emotion in it and because of it, and finally, I noticed pain and the titillation of pleasure in its parts, but not in any objects placed outside it. But why a certain strange sadness of spirit follows a sensation of pain and a certain joy follows from a sensation of [pleasurable] titillation, or why some sort of twitching in the stomach, which I call hunger, is urging me to eat food, while the dryness of my throat [is urging me] to drink, and so on—for that I had no logical explanation, other than that these were things I had learned from nature. For there is clearly no relationship (at least, none I can understand) between that twitching [in the stomach] and the desire to consume food, or between the sensation of something causing pain and the awareness of sorrow arising from that feeling. But it seemed to me that all the other judgments I made about objects of sense experience I had learned from nature. For I had convinced myself that that was how things happened, before I thought about any arguments which might prove it.

However, many later experiences have gradually weakened the entire faith I used to have in the senses. For now and then towers which seemed round from a distance appeared square from near at hand, immense statues standing on the tower summits did not seem large when I viewed them from the ground, and in countless other cases like these I discovered that my judgments were deceived in matters dealing with external senses. And not just with external [senses], but also with internal ones as well. For what could be more internal than pain? And yet I heard that people whose legs or arms had been cut off sometimes still seemed to feel pain in the part of their body which they lacked. Thus, even though I were to feel pain in one of my limbs, I did not think I could be completely certain that it was the limb which caused my pain. To these reasons for doubting sense experience, I recently added two extremely general ones. First, there was nothing I ever thought I was sensing while awake that I could not also think I was sensing now and then while asleep, and since I do not believe that those things I appear to sense in my sleep come to me from objects placed outside me, I did not see why I should give more credit to those I appear to sense when I am awake. Second, because I was still ignorant—or at least was assuming I was ignorant—of the author of my being, there seemed to be nothing to prevent nature from constituting me in such a way that I would make mistakes, even in those matters which seemed to me most true. And as far as concerns the reasons which had previously convinced me of the truth of what I apprehended with my senses, I had no difficulty answering them. For since nature seemed to push me to accept many things which my reason opposed, I believed I should not place much trust in those things nature taught. And although perceptions of the senses did not depend upon my will, I did not believe that was reason enough for me to conclude that they must come from things different from myself, because there could well be some other faculty in me, even one I did not yet know, which produced them.

But now that I am starting to gain a better understanding of myself and of the author of my being, I do not, in fact, believe that I should  rashly accept all those things I appear to possess from my senses, but, at the same time, [I do not think] I should call everything into doubt.

First, since I know that all those things I understand clearly and distinctly could have been created by God in a way that matches my conception of them, the fact that I can clearly and distinctly understand one thing apart from something else is sufficient to convince me that the two of them are different, because they can be separated from each other, at least by God. The power by which this [separation] takes place is irrelevant to my judgment that they are distinct. And therefore, given the mere fact that I know I exist and that, at the moment, I look upon my nature or essence as absolutely nothing other than that I am a thinking thing, I reasonably conclude that my essence consists of this single fact: I am a thinking thing. And although I may well possess (or rather, as I will state later, although I certainly do possess) a body which is very closely joined to me, nonetheless, because, on the one hand, I have a clear and distinct idea of myself, insofar as I am merely a thinking thing, without extension, and, on the other hand, [I have] a distinct idea of body, insofar as it is merely an extended thing which does not think, it is certain that my mind is completely distinct from my body and can exist without it.

Moreover, I discover in myself faculties for certain special forms of thinking, namely, the faculties of imagining and feeling. I can conceive of myself clearly and distinctly as a complete being without these, but I cannot do the reverse and think of these faculties without me, that is, without an intelligent substance to which they belong. For the formal conception of them includes some act of intellection by which I perceive that they are different from me, just as [shapes, movement, and the other] modes [or accidents of bodies are different] from the object [to which they belong]. I also recognize certain other faculties [in me], like changing position, assuming various postures, and so on, which certainly cannot be conceived, any more than those previously mentioned, apart from some substance to which they belong, and therefore they, too, cannot exist without it. However, it is evident that these [faculties], if indeed they [truly] exist, must belong to some corporeal or extended substance, and not to any intelligent substance, since the clear and distinct conception of them obviously contains some [form of] extension, but no intellectual activity whatsoever. Now, it is, in fact, true that I do have a certain passive faculty of perception, that is, of receiving and recognizing ideas of sensible things. But I would be unable to use this power unless some active faculty existed, as well, either in me or in some other substance capable of producing or forming these ideas. But this [active faculty] clearly cannot exist within me, because it presupposes no intellectual activity at all and because, without my cooperation and often even against my will, it produces those ideas. Therefore I am left to conclude that it exists in some substance different from me that must contain, either formally or eminently, all the reality objectively present in the ideas produced by that faculty (as I have just observed above).\footnote{``By [\textit{objective reality of an idea}] I mean the being of the thing which is represented by an idea, in so far as this exists in the idea. . . . For whatever we perceive as being in the objects of our ideas exists objectively in the ideas themselves. . . . Whatever exists in the objects of our ideas in a way which exactly corresponds to our perception of it is said to exist \textit{formally} in those objects. Something is said to exist \textit{eminently} in an object when, although it does not exactly correspond to our perception of it, its greatness is such that it can fill the role of that which does so correspond'' (Descartes, \textit{Objections and Replies} [1641], in \href{https://uncc.primo.exlibrisgroup.com/permalink/01UNCC_INST/14gt3pp/alma991009340179704091}{\textit{The Philosophical Writings of Descartes}} 2: 113--114).} This substance is either a body, that is, something with a corporeal nature which obviously contains formally everything objectively present in the ideas, or it must be God, or some other creature nobler than the body, one that contains [those same things] eminently. But since God is not a deceiver, it is very evident that he does not transmit these ideas to me from himself directly or even through the intervention of some other creature in which their objective reality is contained, not formally but only eminently. For since he has given me no faculty whatsoever for recognizing such a source, but by contrast, has endowed me with a powerful tendency to believe that these ideas are sent out from corporeal things, I do not see how it would be possible not to think of him as a deceiver, if these [ideas] were sent from any source other than corporeal things. And therefore corporeal things exist. However, perhaps they do not all exist precisely in the ways I grasp them with my senses, since what I comprehend with my senses is very obscure and confused in many things. But at least [I should accept as true] all those things in them which I understand clearly and distinctly, that is, generally speaking, everything which is included as an object in pure mathematics.

But as far as concerns other material things which are either merely particular, like that the sun is of such and such a magnitude and shape, and so on, or less clearly understood, like light, sound, pain, and things like that, although these may be extremely doubtful and uncertain, nonetheless, because of the very fact that God is not a deceiver and thus it is impossible for there to be any falsity in my opinions which I cannot correct with another faculty God has given me, I have the sure hope that I can reach the truth even in these matters. And clearly there is no doubt that all those things I learn from nature contain some truth. For by the term \textit{nature}, generally speaking, I understand nothing other than either God himself or the coordinated structure of created things established by God, and by the term \textit{my nature}, in particular, nothing other than the combination of all those things I have been endowed with by God.

However, there is nothing that nature teaches me more emphatically than the fact that I have a body, which does badly when I feel pain, which needs food or drink when I suffer from hunger or thirst, and so on. And therefore I should not doubt that there is some truth in this.

For through these feelings of pain, hunger, thirst, and so on, nature teaches me that I am not only present in my body in the same way a sailor is present onboard a ship, but also that I am bound up very closely and, so to speak, mixed in with it, so that my body and I form a certain unity. For if that were not the case, then when my body was injured, I, who am merely a thinking thing, would not feel any pain because of it; instead, I would perceive the wound purely with my intellect, just as a sailor notices with his eyes if something is broken on his ship. And when my body needed food or drink, I would understand that clearly and not have confused feelings of hunger and thirst. For those sensations of thirst, hunger, pain, and so on are really nothing other than certain confused ways of thinking, which arise from the union and, as it were, the mixture of the mind with the body.

Moreover, nature also teaches me that various other bodies exist around my own and that I should pursue some of these and stay away from others. And certainly from the fact that I sense a wide diversity of colours, sounds, odours, tastes, heat, hardness, and similar things, I reasonably conclude that in the bodies from which these different sense perceptions come there are certain variations which correspond to these perceptions, even if they are perhaps not like them. And given the fact that I find some of these sense perceptions pleasant and others unpleasant, it is entirely certain that my body, or rather my totality, since I am composed of body and mind, can be affected by various agreeable and disagreeable bodies surrounding it.

However, many other things which I seemed to have learned from nature I have not really received from her, but rather from a certain habit I have of accepting careless judgments [about things]. And thus it could easily be the case that these judgments are false—for example, [the opinion I have] that all space in which nothing at all happens to stimulate my senses is a vacuum, that in a warm substance there is something completely similar to the idea of heat which is in me, that in a white or green [substance] there is the same whiteness or greenness which I sense, that in [something] bitter or sweet there is the same taste I sense, and so on, that stars and towers and anything else some distance away have bodies with the same size and shape as the ones they present to my senses, and things of that sort. But in order to ensure that what I perceive in this matter is sufficiently distinct, I should define more accurately what it is precisely that I mean when I say I have learned something from nature. For here I am taking the word \textit{nature} in a more restricted sense than \textit{the combination of all those things which have been bestowed on me by God}. For this combination contains many things which pertain only to the mind, such as the fact that I perceive what has been done cannot be undone, and all the other things I grasp by my natural light [without the help of the body]. Such things are not under discussion here. This combination also refers to many things which concern only the body, like its tendency to move downward, and so on, which I am also not dealing with [here]. Instead, I am considering only those things which God has given me as a combination of mind and body.

And so nature, in this sense, certainly teaches me to avoid those things which bring a sensation of pain and to pursue those which [bring] a sensation of pleasure, and such like, but, beyond that, it is not clear that with those sense perceptions nature teaches us that we can conclude anything about things placed outside of us without a previous examination by the understanding, because to know the truth about them seems to belong only to the mind and not to that combination [of body and mind]. And so, although a star does not make an impression on my eyes any greater than the flame of a small candle, nonetheless, that fact does not incline me, in any real or positive way, to believe that the star is not larger [than the flame], but from the time of my youth I have made this judgment without any reason [to support it]. And although I feel heat when I come near the fire, and even pain if I get too close to it, that is really no reason to believe that there is something in the fire similar to that heat I feel any more than there is something similar to the pain. The only thing [I can conclude] is that there is something in the fire, whatever it might be, which brings out in us those sensations of heat or pain. So, too, although in some space there is nothing which stimulates my senses, it does not therefore follow that the space contains no substances. But I see that in these and in a great many other matters, I have grown accustomed to undermine the order of nature, because, of course, these sense perceptions are, strictly speaking, given to me by nature merely to indicate to my mind which things are agreeable or disagreeable to that combination of which it is a part, and for that purpose they are sufficiently clear and distinct. But then I use them as if they were dependable rules for immediately recognizing the essence of bodies placed outside me. However, about such bodies they reveal nothing except what is confusing and obscure.

In an earlier section, I have already examined sufficiently why my judgments happen to be defective, in spite of the goodness of God. However, a new difficulty crops up here concerning those very things which nature reveals to me as objects I should seek out or avoid and also concerning the internal sensations, in which I appear to have discovered errors: for example, when someone, deceived by the pleasant taste of a certain food, eats a poison hidden within it [and thus makes a mistake]. Of course, in this situation, the person’s nature urges him only to eat food which has a pleasant taste and not the poison, of which he has no knowledge at all. And from this, the only conclusion I can draw is that my nature does not know everything. There is nothing astonishing about that, because a human being is a finite substance and thus is capable of only limited perfection.

However, we are not infrequently wrong even in those things which nature urges [us to seek]. For example, sick people are eager for drink or food which will harm them soon afterwards. One could perhaps claim that such people make mistakes because their nature has been corrupted. But this does not remove the difficulty, for a sick person is no less a true creature of God than a healthy one, and thus it seems no less contradictory that God has given the person a deceitful nature. And just as a clock made out of wheels and weights observes all the laws of nature with the same accuracy when it is badly made and does not indicate the hours correctly as it does when it completely satisfies the wishes of the person who made it, in the same way, if I look on the human body as some kind of machine composed of bones, nerves, muscles, veins, blood, and skin, as if no mind existed in it, the body would still have all the same motions it now has in those movements that are not under the control of the will and that, therefore, do not proceed from the mind [but merely from the disposition of its organs]. I can readily acknowledge, for example, that in the case of a body sick with dropsy, it would be quite natural for it to suffer from a parched throat, which usually conveys a sensation of thirst to the mind, and for its nerves and other parts also to move in such a way that it takes a drink and thus aggravates the illness. And when nothing like this is harming the body, it is equally natural for it to be stimulated by a similar dryness in the throat and to take a drink to benefit itself. Now, when I consider the intended purpose of the clock, I could say that, since it does not indicate the time correctly, it is deviating from its own nature, and, in the same way, when I think of the machine of the human body as something formed for the motions which usually take place in it, I might believe that it, too, is deviating from its own nature, if its throat is dry when a drink does not benefit its own preservation. However, I am fully aware that this second meaning of the word \textit{nature} is very different from the first. For it is merely a term that depends on my own thought, a designation with which I compare a sick person and a badly constructed clock with the idea of a healthy person and a properly constructed clock, and thus, the term is extrinsic to these objects. But by that [other use of the term \textit{nature}] I understand something that is really found in things and that therefore contains a certain measure of the truth.

Now, when I consider a body suffering from dropsy, even though I say that its nature has been corrupted, because it has a dry throat and yet does not need to drink, clearly the word \textit{nature} is merely an extraneous term. However, when I consider the composite, that is, the mind united with such a body, I am not dealing with what is simply a term but with a true error of nature, because this composite is thirsty when drinking will do it harm. And thus I still have to enquire here why the goodness of God does not prevent its nature, taken in this sense, from being deceitful.

At this point, then, my initial observation is that there is a great difference between the mind and the body, given that the body is, by its very nature, always divisible, whereas the mind is completely indivisible. For, in fact, when I think of [my mind], that is, when I think of myself, to the extent that I am only a thinking thing, I cannot distinguish any parts within me. Instead, I understand that I am something completely individual and unified. And although my entire mind seems to be united with my entire body, nonetheless, I know that if a foot or arm or any other part of the body is sliced off, that loss will not take anything from my mind. And I cannot call the faculties of willing, feeling, understanding, and so on parts of the mind because it is the same single mind that wishes, feels, and understands. By contrast, I cannot think of any corporeal or extended substance that my thought is not capable of dividing easily into parts. From this very fact, I understand that the substance is divisible. This point alone would be enough to teach me that the mind is completely different from the body, if I did not already know that well enough from other sources.

Furthermore, I notice that the mind is not immediately affected by all parts of the body, but only by the brain, or perhaps even by just one small part of it, namely, the one in which our common sense is said to exist.\footnote{Aristotle postulated ``a perceptual power over and above the five senses which monitors their states and co-ordinates their reports. This perceptual power [was] known as the `common sense''' (Gregoric, \href{https://uncc.primo.exlibrisgroup.com/permalink/01UNCC_INST/14gt3pp/alma991003759339704091}{\textit{Aristotle on the Common Sense}}, 2). On the small part of the brain to which Descartes was alluding, see Lokhorst, \href{https://plato.stanford.edu/entries/pineal-gland/}{Descartes and the Pineal Gland}.} Whenever this part is arranged in the same particular way, it delivers the same perception to the mind, even though the other parts of the body may be arranged quite differently at the time. This point has been demonstrated in countless experiments, which I need not review here.

In addition, I notice that the nature of my body is such that no part of it can be moved by any other part some distance away which cannot also be moved in the same manner by any other part lying between them, even though the more distant part does nothing. So, for example, in a rope ABCD [which is taut throughout], if I pull on part D at the end, then the movement of the first part, A, will be no different than it would be if I pulled at one of the intermediate points, B or C, while the last part, D, remained motionless. And for a similar reason, when I feel pain in my foot, physics teaches me that this sensation occurs thanks to nerves spread throughout the foot. These nerves stretch from there to the brain, like cords, and when they are pulled in my foot, they also pull the inner parts of the brain, where they originate, and stimulate in them a certain motion which nature has established to influence the mind with a sense of pain apparently present in the foot. However, since these nerves have to pass through the tibia, the thigh, the loins, the back, and the neck in order to reach the brain from the foot, it can happen that, even if that portion of the nerves which is in the foot is not affected, but only one of the intermediate portions, the motion created in the brain is exactly the same as the one created there by an injured foot. As a result, the mind will necessarily feel the identical pain. And we should assume that the same is true with any other sensation whatsoever.

Finally, I notice that, since each of those motions created in that part of the brain which immediately affects the mind introduces into it only one particular sensation, we can, given this fact, come up with no better explanation than that this sensation, out of all the ones which could be introduced, is the one which serves to protect human health as effectively and frequently as possible [when a person is completely healthy]. But experience testifies to the fact that all sensations nature has given us are like this, and thus we can discover nothing at all in them which does not bear witness to the power and benevolence of God. Thus, for example, when the nerves in the foot are moved violently and more than usual, their motion, passing through the medulla of the spinal cord to the inner core of the brain, gives a signal there to the mind which makes it feel something—that is, it feels as if there is a pain in the foot. And that stimulates [the mind] to do everything it can to remove the cause of the pain as something injurious to the foot. Of course, God could have constituted the nature of human beings in such a way that this same motion in the brain communicated something else to the mind, for example, a sense of its own movements, either in the brain, or in the foot, or in any of the places in between—in short, of anything you wish. But nothing else would have served so well for the preservation of the body. In the same way, when we need a drink, a certain dryness arises in the throat which moves its nerves and, with their assistance, the inner parts of the brain. And this motion incites in the mind a sensation of thirst, because in this whole situation nothing is more useful for us to know than that we need a drink to preserve our health. The same is true for the other sensations.

From this it is clearly evident that, notwithstanding the immense goodness of God, human nature, given that it is composed of mind and body, cannot be anything other than something that occasionally deceives us. For if some cause, not in the foot, but in some other part through which the nerves stretch between the foot and the brain, or even in the brain itself, stimulates exactly the same motion as that which is normally aroused when a foot is injured, then pain will be felt as if it were in the foot, and the sensation will naturally be deceiving. Since that same motion in the brain is never capable of transmitting to the mind anything other than the identical sensation and since [the sensation] is habitually aroused much more frequently from an injury in the foot than from anything else in another place, it is quite reasonable that it should always transmit to the mind a pain in the foot rather than a pain in any other part of the body. And if sometimes dryness in the throat does not arise, as it usually does, from the fact that a drink is necessary for the health of the body, but from some different cause, as occurs in a patient suffering from dropsy, it is much better that it should deceive us in a case like that than if it were, by contrast, always deceiving us when the body is quite healthy. The same holds true with the other sensations.

This reflection is the greatest help, for it enables me not only to detect all the errors to which my nature is prone, but also to correct or to avoid them easily. For since I know that, in matters concerning what is beneficial to the body, all my senses show [me] what is true much more frequently than they deceive me, and since I can almost always use several of them to examine the same matter and, in addition, [can use] my memory, which connects present events with earlier ones, as well as my understanding, which has now ascertained all the causes of my errors, I should no longer fear that those things which present themselves to me every day through my senses are false. And I ought to dismiss all those exaggerated doubts of the past few days as ridiculous, particularly that most important [doubt] about sleep, which I did not distinguish from being awake. For now I notice a significant distinction between the two of them, given that our memory never links our dreams to all the other actions of our lives, as it [usually] does with those things which take place when we are awake. For clearly, if someone suddenly appears to me when I am awake and then immediately afterwards disappears, as happens in my dreams, so that I have no idea where he came from or where he went, I would, not unreasonably, judge that I had seen some apparition or phantom created in my brain [similar to the ones created when I am asleep], rather than a real person. But when certain things occur and I notice distinctly the place from which they came, where they are, and when they appeared to me, and when I can, without any interruption, link my perception of them to the rest of my life as a totality, then I am completely certain that this is taking place while I am awake and not in my sleep. And I should not have the slightest doubt about the truth of these perceptions if, after I have called upon all my senses, my memory, and my understanding to examine them, I find nothing in any of them which contradicts any of the others. For since God is not a deceiver, it must follow that in such cases I am not deceived. But because, in dealing with what we need to do, we cannot always take the time for such a scrupulous examination, we must concede that human life is often prone to error concerning particular things and that we need to acknowledge the frailty of our nature.

\end{document}  