It is from the views of Descartes that most of the metaphysical systems of the last three centuries begin, trying to improve upon them, or to overcome what they regard as difficulties in the Cartesian system. Ren Descartes is responsible for the predominance of the problem of human knowledge in modern philosophy. Many of the systems of philosophy and theories of knowledge which have arisen in the last three centuries can trace their lineage directly to the influence of the questions Descartes raised and the method he employed in answering them.
He promulgated the principle of “science without presuppositions” and thereby introduced a new epoch in science and philosophy. It will, therefore, not be amiss to analyze his fundamental ideas and evaluate his method. As his starting point Descartes begins with the contention that we rely entirely too much on traditional doctrines and spontaneous convictions, so that our supposed knowledge of truth rest mostly on unproved presuppositions. This makes it difficult for us to distinguish between truth and error, since we do not know what is true knowledge and what is unwarranted belief.
Hence, he would tear down the whole edifice of knowledge and rebuilt it from the foundation, and he would not begin to build until he had reached the one and ultimate truth which the bedrock of human knowledge. Being a mathematician, Descartes felt convinced that he could deduce all truth from a single fundamental principle. As the instrument of his search for truth he used a universal methodic doubt. His own words will best reveal his line of thought. I.
In order to seek truth, it is necessary once in the course of our life, to doubt, as far as possible, of all things. As we were at one time children, and as we formed various judgments regarding the objects presented to our senses, when as yet we had not the entire use of our reason, numerous prejudices stand in the way of our arriving at the knowledge of truth; and of these it seems impossible for us to rid ourselves, unless we undertake, once in our lifetime, to doubt of all those things in which we may discover even the smallest suspicion of uncertainty.
II. We ought also to consider as false all that is doubtful. Moreover, it will be useful likewise to esteem as false the things of which we shall be able to doubt, that we may with greater clearness discover what possesses most certainty and is easiest to know. III. We ought not meanwhile to make use of doubt in the conduct of life… IV. Why we may doubt of sensible things.
Accordingly, since we now only design to apply ourselves to the investigation of truth, we will doubt, first, whether of all the things that have ever fallen under our senses, or which we have ever imagined, any one really exists; in the first place, because we know by experience that the senses sometimes err, and it would be imprudent to trust too much to what has even once deceived us; secondly, because in dreams we perpetually seem to perceive or imagine innumerable objects which have no existence.
And to one who has thus resolved upon a general doubt, there appear no marks by which he can with certainty distinguish sleep from the waking state. V. Why we may also doubt of mathematical demonstrations.
We will also doubt of the other things we have before held as most certain, even of the demonstrations of mathematics, and of their principles which we have hitherto deemed self-evident; in the first place, because we have sometimes seen men fall into error in such matters, and admit as absolutely certain and self-evident what to us appeared false, but chiefly because we have learned that God who created us is all-powerful; for we do not yet know whether perhaps it was His will to create us so that we are always deceived, even in the things we know best: since this does not appear more impossible than our being occasionally deceived, which, however, as observation teaches us, is the case. And if we suppose that an all-powerful God is not the author of our being, and that we exist of ourselves or by some other means, still, the less powerful we suppose our author to be, the greater reason will we have for believing that we are not so perfect as that we may not be continually deceived… VII. We cannot doubt of our existence while we doubt, and this is the first knowledge we acquire when we philosophize in order.
While we thus reject all of which we can entertain the smallest doubt, and even imagine that it is false, we easily indeed suppose that there is neither God, nor sky, nor bodies, and that we ourselves have neither hands nor feet, not, finally, a body; but we cannot in the same way suppose that we are not while we doubt of the truth of these things; for there is a repugnance in conceiving that what thinks does not exist at the very moment when it thinks. Accordingly, the knowledge, “I think, therefore, I am,” is the first and most certain that occurs to one who philosophizes orderly. (1) This is indeed a most radical procedure, a veritable revolution of method. Descartes applied the method of universal doubt to “all things,” attempting to empty the mind completely of all traditional views, preconceived ideas, and spontaneous convictions without exception. Nothing is allowed to remain, no matter how seemingly clear and evident. Even the simplest arithmetical and geometrical problem is not permitted to stand, like “2+3=5” and “a square has but four sides.
As he expresses himself: “How do I know that I am not also deceived each time I add together two and three, or number the sides of a square, or form some judgment still more simple, if more simple indeed can be imagined? ” (2) Not only the whole physical world, our own body, sense-perception, and the internal states of our consciousness, are thus drawn into universal doubt, but also the trustworthiness of our cognitive faculties and the fundamental laws of thinking, like the principle of sufficient reason and the principle of contradiction. This a most important feature of his method that must not be overlooked. Descartes’ universal methodic doubt is not merely simulated for the sake of an unprejudiced search after truth; it is a real, genuine doubt. ”
As I desired to give my attention solely to the search after truth, I thought… at I ought to reject as absolutely false all in regard to which I could suppose the least ground for doubt, in order to ascertain whether after that there remained aught in my belief that was wholly indubitable. ” (3) Mark the words: “to reject as absolutely false. ” He does not intend to hold his mind in a state of suspended judgment, or merely to leave his spontaneous convictions aside for the time being, in order to investigate their possible validity, which would be methodic doubt as generally understood; he is convinced that he ought “to reject them as absolutely false,” and he actually carries out his plan, so that he really rejects everything down to the one indubitable fact: “Cogito, ergo sum — I think, therefore I exist. ”
This is more than mere doubt, because a doubt presupposes a suspended judgment due to the absence of all reasons for and against a proposition (negative doubt) or reasons of more or less equal value for an against it (positive doubt). Descartes “supposes, for a time, that all these opinions are entirely false and imaginary,” (4) and he “will continue always in this track until he shall find something that is certain, or at least, if he can do nothing more, until he shall know with certainty that there is nothing certain. ” (5) He assumes the attitude that all spontaneous convictions and laws of thought are errors. It makes little difference whether Descartes could and did, actually and really, doubt everything without exception; or whether he merely thought he could and did.
The fact is, he did thus doubt everything in principle. He was, of course, not a skeptic, since his purpose was to arrive at the ultimate base of certainty and truth and to rebuild on this indubitable foundation the edifice of knowledge. He compared himself to Archimedes. “Archimedes, that he might transport the entire globe from the place it occupied to another, demanded only a point that was firm and immovable; so also, I shall be entitled to entertain the highest expectations, if I am fortunate enough to discover only one thing that is certain and indubitable. ” (6) Descartes was fortunate enough to discover his firm and immovable fulcrum: his own existence — “I think, therefore I am.
He had now his fulcrum; what would be his lever? It would have to be the trustworthiness of his reasoning powers. But how could he establish this, seeing that this also was involved in universal doubt and destroyed with all other spontaneous convictions? Descartes hit upon an ingenious idea. He would demonstrate the existence of an infinitely perfect Being, who must have given man faculties which are trustworthy and capable of discovering truth. The only thing absolutely certain so far for Descartes was his own existence; and from this fact alone he would be obliged to deduce God’s existence. ? We have in our mind the idea of God as an infinitely perfect Being.
But an infinitely perfect Being must have existence, otherwise it would not be infinitely perfect. This is an a priori or ontological argument. Descartes attempts to prove God’s existence a posteriori, by means of an argument from causality: ? We have the idea of God in our mind. ? Since this idea represents an infinitely perfect Being, we, as finite beings, cannot have originated such an idea in virtue of our own powers. ? This idea being beyond our mental capacity, it could have originated only from a Being who possesses such infinite perfection. Having proved to his own satisfaction that God exists, Descartes proceeds to show that He is the creator of man. )
But the infinitely perfect God cannot be a deceiver; consequently, He cannot have given man deceptive powers of knowledge, and man’s faculties are thus shown to be trustworthy, “provided we separate what there is of clear and distinct in the knowledge from what is obscure and confused. ” (10) In the light of this criterion of “clear and distinct” knowledge all previous doubts about the world, sense-perception, and intellection must vanish. Skepticism is defeated, and valid knowledge is possible. Descartes’ fundamental purpose was laudable; he desired to defend human knowledge against the attacks of skeptics. Generally speaking, he was justified in demanding that the investigation into the nature and limits of knowledge exclude preconceived ideas, traditional doctrines, and unwarranted presuppositions as evidence and proof, since the validity of all spontaneous convictions was at stake.
But when he proposed to approach the problem in an attitude of universal real doubt, discarding even the capability of the human mind to know truth and refusing to accept such essential principles as the principle of contradiction and the principle of sufficient reason, he made the solution of the problem impossible for himself. Here are a few considerations which compel us to reject his system. Descartes began his inquiry by doubting all knowledge without exception; he was even willing to accept it as “entirely false. ” This being the case, what about the idea of God as an all-perfect Being, since he admits that he discovered this idea in his own mind? According to his own principle of universal doubt, he simply cannot know whether this idea of God is correct or incorrect; as a matter of fact, according to this principle, he should consider it as “entirely false,” until proved otherwise.
But if his idea of God as an all-perfect Being may be incorrect, he cannot logically deduce from this idea God’s existence and veracity. Since the very idea of God is doubtful, these other things must remain doubtful, and the trustworthiness of man’s faculties must also remain doubtful. Descartes cannot escape his own real doubt. Irrespective of the intrinsic value of the proofs with which Descartes attempts to demonstrate God’s existence, we must not overlook the fact that he uses a process of reasoning to make this demonstration. Since his very reason and the process of reasoning is as yet of doubtful validity, how can be validly demonstrate God’s existence and veracity?
The trustworthiness of Descartes’ reasoning powers is supposed to flow as a necessary consequence from the infinite perfection of God; and God’s infinite perfect is made certain to him by means of a proof developed by these very reasoning powers, before he has proved that these reasoning powers are valid and trustworthy: he thereby gratuitously assumes the very thing beforehand which he intends to prove afterwards. (A logical fallacy called Begging the Question, or a circular argument. ) Descartes unconsciously accepts the trustworthiness of his faculties in attempting to demonstrate the existence and infinite perfection of God, and that is an illegitimate procedure; because a doubtfully valid faculty can produce only a doubtfully valid argument, and a doubtfully valid argument can only lead to a doubtfully valid conclusion.
The whole argument for God’s existence and veracity is thus nullified by his doubtful reason and reasoning process; and, since he proves the reliability of his reason and reasoning process by means of God’s veracity, which (according to his supposition) must be doubtful, the proof for the trustworthiness of his own powers is nullified and can never be established beyond doubt. His attempt, therefore, to vindicate the validity of human knowledge failed essentially, because, by rejecting the reliability of his own powers to discover and know truth, he made it impossible for himself to extricate himself from the net of his own universal doubt. Moreover, there are glaring inconsistencies in his procedure. He claims to reject everything, even the principle of contradiction and the principle of sufficient reason. But he does not. He surreptitiously assumes the truth of these principles and uses them continually.
As obvious a fact as the “Cogito, ergo sum” is really based on the validity and truth of the principle of contradiction. This principle asserts that it is impossible for something to be and not to be at the same time. Descartes becomes certain of his own existence by the very fact of his “thinking” or “doubting. ” True. But why? Because he perceives clearly that it is impossible to “think and not think,” to “exist and not exist” at the same time. If Descartes were consistent and really doubted the principle of contradiction, he would have to affirm that it could be possible for a being to “think and not think,” to “exist and not exist” at the same time.
But, then, according to his own supposition, he could not be sure after all that the ultimate fact of his existence is certain, and his famous “Cogito, ergo sum” has no real objective value. Only by granting the validity and truth of the principle of contradiction beforehand, can his existence be established as an objective fact; and that is exactly, though inconsistently, what Descartes does. The same line of reasoning applies to his proofs for God’s existence and infinite perfection. Notwithstanding his proofs, his rejection of the principle of contradiction will forever invalidate his arguments, because, as long as this principle is not established and accepted, he could never be sure whether it would not be possible for God to “exist and not exists,” to “be infinitely perfect and not infinitely perfect” at the same time.
Similarly, he would always be compelled to remain in doubt whether God could not be “veracious and not veracious,” “deceiving and not deceiving,” unless the principle of contradiction were taken as granted before he begins to prove God’s existence. Unwittingly Descartes does accept this principle of contradiction throughout his demonstrations, but that is an inexcusable inconsistency. So, too, Descartes conducts his inquiry under the supposition that he has doubted the principle of sufficient and the principle of causality. But he does not hesitate to use these principles before he has established their validity. Consider his a posteriori argument for the existence and infinite perfection of God.
He contends that the idea of God as an all-perfect Being could not have originated in our mind, because such an idea would exceed the causality of the human mind, the latter being less perfect than the contents of the idea itself; consequently, this idea had to be produced in us by God Himself (and this proves that God exists as an infinitely perfect Being), otherwise there would be no sufficient reason for the presence of such an idea in our mind. This line of reasoning shows plainly that Descartes uses the principles of sufficient reason and causality in demonstrating God’s existence, although he doubts their validity. Now, if he lets these principles stand as doubtful, his entire demonstration is vitiated and nullified by doubt; and if he accepts them as valid prior to establishing their validity, he acts contrary to his fundamental doubt and is inconsistent: in either case he makes the demonstration of God’s existence impossible.
His actual procedure in all the arguments he makes is such, however, that he presupposes the validity of the laws of thought; and that is for him a glaring inconsistency, since his universal methodic doubt will not permit him to accept their validity before he has proved the existence and veracity of God. Finally, Descartes’ universal methodic doubt leads logically to universal skepticism. No certitude can ever be attained in a system where the very foundations of human reason are completely destroyed. When he rejects as doubtful and even as “absolutely false” all in regard to which he could imagine the least ground for doubt, he saws off the very limb upon which he is seated.
If the nature of his mind and the laws of thought are called into real doubt (not to speak of considering them to be “absolutely false”), then all acts and facts of consciousness, all ideas, judgments, and inferences, can no longer be trusted. But how can the mind attempt to validate its own trustworthiness except by means of these things? If Descartes mistrusts the simple judgments of “2+3=5” and “A square has four sides,” how can he trust his faculties in making the far more complicated arguments with which he tries to prove God’s existence and infinite perfection? The effort of Descartes to find his way back to certitude by means of the roundabout detour of the existence and veracity of God, shows the desperate plight in which he had placed himself by his universal doubt. The steps he takes in retracing his way are these: ? The existence and infinite perfection of God; ?
The trustworthiness of his faculties, due to the veracity of God who created him; The truth and validity of all those spontaneous convictions of his mind which are “clear and distinct. ” But we have seen that Descartes could not consistently prove God’s existence, since he could only do so by means of a reasoning process which, according to his own principles, was essentially doubtful in its validity, and even “absolutely false. ” The only thing of which he could ever be certain was his own existence; and this, too, strictly speaking, Descartes should have doubted, because he had doubted the principle of contradiction and the testimony of his own consciousness. Our modern Archimedes had indeed found his fulcrum, namely his own existence; but now he could not move the world, because he had thrown away his lever.
Descartes, if he had been consistent, should have embraced universal skepticism, because his universal doubt left him no other choice: he had no way of retracing his course. He was like a mariner who scuttles his boat and swims to a rock in mid-ocean. The rock is the solitary fact of his own existence. True, he had found a solid point. But it is a lonely and desolate spot; and he is marooned on it forever, doomed to die of mental starvation, surrounded by an unbridgeable ocean of doubt. The Cartesian universal methodic doubt, therefore, is not a proper approach to the problem of human knowledge. It is in reality only a variation of universal skepticism, and as such it is absurd.
We will have to make our approach in a different fashion. The necessary conclusion to be drawn from the above critical examination of universal skepticism is obvious: Complete doubt cannot be the proper approach to the problem of human knowledge. It would be fatal. Starting with complete doubt, we can no more reach a solution of the problem of human knowledge than a bird can fly with amputated wings. Another important conclusion is this: Any theory of knowledge which leads logically to universal skepticism is intrinsically false. Nothing could be plainer. There must be an essential flaw in a theory which, if consistently carried out to its logical conclusions, ends in the absurdity of skepticism.