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Before entering upon the propositions themselves and their proofs, it seemed fitting to offer a succinct explanation why Descartes questioned everything, in what manner he discovered the firm foundations of knowledge, and finally by what means he freed himself from all his doubts. All this matter we should certainly have reduced to a mathematical orderliness, had we not considered the prolixity necessary for its presentation a hindrance for a proper understanding of the entire subject that ought to be viewed, as in the case of a picture, by a comprehensive survey.
Descartes, then, proceeding with the utmost caution in the investigation of nature, attempted:
1. to reject all pre-conceived notions;
2. to find the bases for all necessary superstructures;
3. to discover the cause of error;
4. to understand everything clearly and distinctly.
In order to attain the first, second, and third objectives, he proceeds to question everything; not indeed as a skeptic, for whom the final end is nothing but doubt, but with a view to freeing his mind from all pre-conceptions and hence to discover ultimately the solid and irrefutable bases of knowledge that he could not fail to discover, if such exist. For the true principles of knowledge must be so lucid and convincing that they require no proof, exclude all risk of doubt, and make any proof impossible without them. After prolonged doubt, Descartes discovered such principles. Upon their discovery, it was not difficult for him to distinguish truth from falsity, to discover the cause of error, and furthermore to take precautions not to assume what is false and doubtful as truth and certainty.
To reach the fourth and last objective, that is, to understand clearly and distinctly, his principal rule was to review all the simple ideas, of which all the others are composed, and to examine them severally. For if he could perceive simple ideas clearly and distinctly, he would doubtless understand all the other ideas composed of these simple ones, with the same clarity and perspicuity. With these preliminary remarks, we shall briefly explain how Descartes called everything into question, found the true principles of knowledge, and liberated himself from the difficulties of doubt.
First of all he considers all things perceived by the senses, namely: heaven, earth, and such notions, and even his own person; all these things he had until then believed to exist in the scheme of Nature. And he doubts their certainty, because his own senses had sometimes deceived him and in his dreams had often convinced him that many things really had an objective existence that he had afterward discovered to be illusory; and finally because he had heard others, even in waking moments, assert that they felt pain in limbs that they had long since lost. Therefore it was not without reason that he was able to doubt the existence even of his own body.
From all these circumstances he was able to deduce rightly that the senses were not a very strong foundation on which to build the superstructure of all knowledge—for they can be called in question—but that certainty depends on other, more convincing principles. To pursue such speculations further, he next considers all the universals, such as material nature in general and its extent, likewise shape, quantity, and so on, and also all the mathematical truths. Although these ideas seemed to him more convincing than all those that he had experienced by the sense, he still found a reason for doubting them; since others too had been mistaken about them, and particularly since a certain old notion had been implanted in his mind that a God existed, all-powerful, by whom he had been created just as he was, and who had perhaps made it possible for him to be deceived about those ideas that seemed very clear to him. By this means he questioned everything.
Discovery of the Basis of All Knowledge
To discover the true principles of knowledge, he investigated next whether he had called into question everything that could come within his thought: thus he would examine whether there was not something left perhaps that he had not yet doubted. If indeed he found anything, by such a method of doubting, that could not be called in question for any of the preceding reasons, or for any other reason, he rightly considered that he could accept it as a basis on which to build the superstructure of all his knowledge. And although he now appeared to doubt everything—for he had doubted equally both the notions that he had received through the senses, and those that he perceived through comprehension only—still there was something left to be examined, namely, himself who doubted thus; not in so far as he was composed of a head, hands, and other members of the body, all matters of doubt; but only in so far as he doubted, thought, and so on.
After a careful examination, he realized that he could entertain doubt on this point for none of the previously mentioned reasons. For, whether the thinking process persists in sleep or in wakefulness, he still thinks and is; whether others were in error about other subjects, or even himself, none the less they existed, since they were in error. Nor could he imagine any author of his own nature, however cunning, who could deceive him in this regard; for it must be granted that he himself existed as long as he supposed himself to be deceived. Finally, whatever other cause for doubt might be conceived, none could be adduced that did not at the same time make him overwhelmingly certain of his own existence. Furthermore, adducing more reasons for doubt meant adducing also more proofs to convince him of his own existence. So much so, that wherever he turned to doubt, he was none the less constrained to exclaim: I doubt, I think, therefore I am.
With the discovery of this truth he likewise found the basis of all the sciences; and even a standard and rule for all the other truths, namely: Whatever is perceived as clearly and distinctly as this truth is true.
That no other basis for knowledge than this is possible is abundantly and more than sufficiently clear from what has preceded, since all the other notions can most readily be called in question, but this one cannot be questioned in any manner whatever. However, in regard to this principle, it must first of all be observed that the statement I doubt, I think, therefore I am is not a syllogism, whose major premise has been omitted. For, if it were a syllogism, the premises ought to have been clearer and better known than the conclusion itself, therefore I am: and so I am would not be the first basis of all knowledge; besides, it would not be a certain conclusion, for its truth would depend on universal premises that the author had long since called in question. So I think, therefore I am is a single proposition, equivalent to this one: I am a thinking being.
Furthermore, to avoid confusion in what follows (for the matter must be perceived clearly and distinctly), we must understand what we are. For, once this is clearly and distinctly understood, our being will not be confused with others. To deduce this therefore from what precedes, our author thus continues.
He recalls in memory all the thoughts that he once had regarding himself: that his soul was a subtle body similar to wind, fire, or air, pervading the thicker parts of the body; that his body was more familiar to him than his soul, and that he had a clearer and more distinct perception of it. He found that all this was manifestly at variance with what he had until then understood. For it was possible for him to doubt his body, but not his existence in so far as he could think. Moreover, not perceiving this clearly or distinctly, he consequently had to reject it as false, according to the method that he had proposed for himself. Hence, since he could not, considering what he already knew of himself, recognize the relation of these questions to himself, he proceeded to investigate further what properly belonged to his being, what he had been unable to doubt, and on account of which he was forced to affirm his existence.
Such are the following notions: He must beware of self-deception; he wanted to comprehend many concepts; he questioned everything that he could not comprehend; up to this time he had posited one truth only; he denied everything else, rejecting it as false; even in spite of himself he imagined many things; finally, he observed many things that appeared to come from the senses. Since, equally evidently, his existence rested on each one of these assertions and since he was unable to view any one of them as among the ideas that he had questioned, and finally since they could all be conceived under the same attribute, it followed that they were all truths and belonged to his nature. And so, in saying I think, he understood all these modes of thought: doubt, understanding, affirmation, denial, wishing, not wishing, imagination, and feeling.
It must first of all be observed—and this will be very useful in what follows, where the distinction between mind and matter is discussed:
1st. These modes of thought are clearly and distinctly comprehended without other questions that are still in doubt.
2nd. The clear and distinct concept that we have of these modes of thought is rendered obscure and confused, if we wish to add to them something that still remains in doubt.
Release from All Doubts
Finally, to reach assurance on what he had questioned and to remove all doubt, he proceeded to inquire into the nature of the most perfect Being and on its existence. For, upon discovering the existence of a most perfect Being, by whose power all things are produced and conserved, and whose nature refutes the possibility of his being an impostor, the reason for doubt, that he entertained through his ignorance of his true cause, will be eliminated. For he will know that the faculty of distinguishing the true from the false was not given to him by a God supremely good and veracious to produce deception. And so the mathematical truths and all those things that appear very evident to him will not admit of any suspicion whatever. Then he advances a step forward to eliminate the other causes of doubt and inquiries: How does it happen that we are sometimes mistaken? When he discovered that this arises from our own use of free will in giving assent even to what we perceived only confusedly, he was at once able to conclude that he could avoid error in the future, provided he gave assent to clear and distinctive perceptions only. Each one may easily achieve this of his own accord, since he has the power of restraining his will and confining it within the limits of the understanding. But as, in early youth, we acquire many preconceptions from which we are not easily liberated, he proceeds, in order to free us so that we accept nothing that we do not clearly and distinctly perceive, to review all the simple notions and ideas, of which all our thoughts are composed; to examine each one separately, in order to discover whatever is obscure in each of them. Thus he will be in a position to make an easy distinction between what is clear and what is obscure, and from clear and distinct thoughts, and so to discover easily the real distinction between the soul and the body: what is clear and what is obscure in the perceptions that we experience by the senses; and lastly, the difference between sleep and wakefulness. Thereupon, he could no longer doubt his wakeful periods or be deceived by the sense; and thus he emancipated himself from all the doubts previously considered.
But, before I stop at this point, I must, it appears, give a satisfactory reply to those who argue as follows: Since the existence of God is not known to us by itself, it does not seem that we can ever be certain of anything: nor will the existence of God ever be known to us. For from uncertain premises (and we saw that everything is uncertain as long as we are unaware of our origin) no certainty can be reached.
To resolve this difficulty, Descartes replies thus: From the fact that we do not yet know whether perhaps the author of our origin has treated us such as to be deceived, even in what appears to us most evident, we cannot in the slightest degree doubt what we know clearly and distinctly by itself, or by reasoning, so long as we give our attention to it; we can doubt only what we previously proved to be true, the memory of which can recur, when we no longer regard the reasons that led to these conclusions and which we have forgotten. Therefore, although the existence of God can be known not by itself but only by some other thing, we shall still be able to attain positive knowledge of God's existence, provided we pay the most careful attention to all the premises from which we draw this conclusion. See Principles, Part I, article 13, and the Response to the Two Objections, No. 3 and the end of the Fifth Meditation.
But, since this reply does not satisfy certain questioners, I shall offer another one. We have seen in the preceding arguments, when we spoke of the certainty and the evidence of our existence, that we reached this conclusion from the fact that, in whatever direction we turned our mental gaze, we encountered no reason for doubt that did not assure us, by that very fact, of our existence; whether we considered our own nature, or whether we imagined the author of our nature as a cunning impostor, or finally whether we appealed to any other reason for doubt outside ourselves; a condition that we never hitherto found present in any other matter. For, although, if we consider the nature of, for example, the Triangle, we are forced to conclude that its three angles are equal to two right angles, we cannot however draw the same conclusion from the fact that perhaps we are deceived by the author of our nature: whereas we thus reached the most certain conclusion of our existence. Therefore we are not forced to conclude, wherever we turn our mental gaze, that the three angles of a Triangle are equal to two right angles, but on the contrary we find a reason for doubt, because we have no idea of God such as to make us think it is impossible for God to be an impostor. For it is just as easy for one who does not have a true idea of God, that we now suppose we do not have, to conceive his author as an impostor or as not an impostor: just as, for the person who has no idea of a Triangle, it is as easy to conceive its three angles as equal or as not equal to two right angles.
Hence we grant that, apart from our existence, we cannot be absolutely certain of anything, however carefully we consider its demonstration, so long as we have no clear and distinct conception of God that obliges us to declare that God is supremely veracious, just as the idea that we have of the Triangle forces us to conclude that its three angles are equal to two right angles; but we deny that we cannot on that account attain a knowledge of anything. For, as is clear from all that has just been said, the crux of the entire question rests on this point only: that we can form a concept of God that does not induce us to conceive him, equally well, as being an impostor, but that forces us to affirm that he is supremely veracious. For as soon as we form such an idea, the reason for doubting the mathematical truths is removed. For, wherever we turn our mental gaze, to question any of these truths, we shall encounter nothing from which we ought not to conclude that this truth is quite certain, as in the case of our existence. For example, if, after attaining the idea of God, we carefully consider the nature of the Triangle, this idea will compel us to assert that its three angles are equal to two right angles; but if we consider the idea of God, it will force us to assert that he is supremely veracious, the author and the continuous preserver of our nature and hence does not deceive us in regard to this truth respecting the Triangle.
Excerpted from Principles of Cartesian Philosophy by Baruch Spinoza, Harry E. Wedeck. Copyright © 1961 Philosophical Library, Inc.. Excerpted by permission of Philosophical Library.
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