RENE DESCARTES’ METHODS OF DOUBT
Introduction
The theory of knowledge and analytical method advanced by the French philosopher Rene Descartes is often summed up in the famous phrase, Cogito ergo sum- “I think, therefore I am.” While this phrase does express the final step in his systematic process of “doubting everything,” it is a gross over-simplification of Descartes’ methods. Descartes did use systematic doubt to find the starting point for his theory of knowledge, but his other philosophical inquiries involved several different methods of doubting, from simply imagining that which is contradictory, to carrying logical postulates to absurd conclusions, to the more traditional methods of testing syllogisms and analyzing proofs. In this essay, I will examine Rene Descartes’ various methods of doubt, to show that the philosopher did not rely on the single reductio ad absurdum in his famous proof of his own existence. Descartes, as we will see, employed several different approaches to philosophical proofs, and he was not the mechanistic logician that his mathematical background might suggest. It will be the argument of this essay that Descartes applied different methods of doubt to different problems, depending upon whether the problem was epistemological, scientific or theological in nature.
Existential Doubt: Do I Exist?

The first and best-known method of doubt employed by Descartes involves reductionism, in the sense that he used a negative or reverse logical path to get to his first most basic principle. In the Meditations on First Philosophy, he first distinguished between the categories of knowledge, arguing that there are some types of knowledge which are subject to illusion or imprecision and some which are not. The basic “knowledge of things in which we have apparent certainty includes...corporeal nature in general, and its extension, the figure of extended things, their quantity or magnitude and number, as also the place in which they are, the time which measures their duration.” (Wilson, 1969:168) Descartes is not, however, proposing that knowledge of such things is proven to the extent that is required by "first philosophy," or pure epistemology. He acknowledges, for example, that an all-powerful controlling deity might have created all of his sensory perceptions, and that the world and all its things might be a vast illusion. An evil all-powerful deity might even be able to make him falsely believe in his own reality, and to believe in a God that was good. Virtually everything can be doubted on this basis, except that an illusion, or some form of mental activity, is taking place. So rigorous epistemology requires that we must doubt the reality of our own perceptions and ideas. Descartes solved this problem by reducing everything that we could know for certain to the simple fact of our consciousness: I must exist because I am experiencing the world. Whatever this experience means, it is undoubtedly taking place, and this phenomenological fact is the only thing of which we can be absolutely certain. But Descartes also realized that beyond this point he could be certain of almost nothing. His mental experience might prove that he (or some thing experiencing mental events) existed, but it proved nothing more than that. He might be the victim of a cosmic hallucination, an evil trick of a malevolent god, or a reflective image or mirage of other type of phenomenon. For all these reasons, Descartes also argued for the important of empirical experiment, not just for science but also for the logic of critical thinking. Beyond the barest fact of existence, tests, logical analysis and empirical data collection are needed. And for this, a different method of doubt- scientific method-is needed.
Scientific Empirical Doubt: What Is Real?
The goal of all epistemology is to attain sure knowledge. Descartes established a number of criteria for certainty of knowledge, and distinguishes between various fields of knowledge and the kind and degree of certainty that we can have in them. Although Descartes was mainly concerned with arriving at a starting point for his reasoning (hence the name of the work), he is also concerned with clarifying his epistemology to the point that he can build some basic categories of knowledge and experiment. Since he intends to subject everything to the scrutiny of doubt, it might seem that a distinction between corporeal and abstract reality is unnecessary, but in fact Descartes needed to develop this mind-body dualism in order to justify his reasoning.
Descartes’ scientific doubt led to his creation of new standards for experimental procedure, such as repeated trials and other tests of reliability and validity. He discovered the cumulative nature of experimental discovery: "I noticed, in regard to experiments, that they become more necessary as one becomes more advanced in knowledge. For in the beginning, it is better to make use only of what presents itself to our senses of its own accord and which we could not ignore, provided we reflect just a little on it, than to search for unusual or contrived experiments" (Descartes, 1969:36).
Descartes goes on to argue that the existence of clear and distinct knowledge of things proves the existence of absolute or abstract knowledge or truths. For example, the pre-existence of the idea of a triangle is proven by the fact that he can imagine it independently of any existing triangle, since it has a "determinate nature, form or essence, which is immutable or eternal..." (Wilson, 1969: 203). He had already included a broader class of things susceptible to certain knowledge, including "numbers, figures, movements, and other such things..." which seem to be recollections of things already known, and thus certain. Shortly afterward, however, he returns to limiting his clear knowledge to "figures, numbers, and other matters which pertain to arithmetic and geometry, and in general, to pure and abstract mathematics." (P. 203) In spite of this discrepancy, Descartes includes motion among the things of which he has a clear and distinct knowledge, as opposed to taste, smell, feel and sensations of heat, thirst, hunger and so on. Descartes' final answer this question is based on his description of the brain as the final organ in the physical chain of movements which bring sensation to consciousness. He remarks in Meditation VI that his "knowledge of physics" tells him that all perception must come via a chain of motion which transmits sensation the brain. We only imagine that the pain we feel when we burn our foot is actually taking place at the foot. In the same way, our perception of movement of matter is ultimately grounded in a sensory process where light strikes the eyes, is transformed into nervous impulses and ends in the visual image in the mind. So the doubt which Descartes applies to external sensation might properly be applied to movement, which does not really belong in the same category of abstract knowledge as geometry and arithmetic- the pure, abstract forms of intellect.
Metaphysical Doubt: Does God Exist? One of the traditional problems in medieval philosophy was the proof of God’s existence, and because empirical science, systematic doubt and metaphysical speculation were still considered heretical in Descartes day, he probably felt it necessary to demonstrate his orthodoxy. Descartes attempts to apply his same basic method of analysis to this problem of God’s existence, but winds up accepting a purely formal, logical proof. He begins, in his Discourse on Method, by declaring that all people possess the innate common sense that should allow them to see truth: “Good sense is the most evenly shared thing in the world, for each of us thinks that he is so well endowed with it that even those who are the hardest to please in all other respects are not in the habit of wanting more than they have...the capacity to judge correctly and to distinguish the true from the false...is naturally equal in all men...Descartes, 1969:27) Descartes assumes that the disagreements men have about the truth come from a failure to properly apply this natural intelligence. Descartes inherited the medieval conceptions of the definition of God, and looking at his own power of reason and particularly at the doubts he entertained about systematic philosophy in general, decided that if the idea of a more perfect being can exist, it must have its origin in an existing more perfect being-- God: “I had learned to think of some thing more perfect than myself; and I clearly recognized that this must have been from some nature which was in fact more perfect. (Descartes, 1969: 55.)This is the same form of reasoning he used to arrive at the famous "Cogito ergo sum," as described above, First he has an idea, thought or perception in his mind, which leads him to knowledge of a truth, since insofar as an idea is real it must have some basis in another reality. Descartes' proof of God’s existence, unfortunately, does not hold to the same rigorous standards as his proof of his own existence. It is based on a priori assumptions of a created consciousness and a rigid relationship between that mind and the creator. In essence, it is an ontological proof for existence as essence, starting from a mental concept and “proving” that the object of the idea must exist if the idea exists. God is defined as that Being “than which none greater can be conceived,” and since it is always to conceive of greater being than an imagined idea, God must exist, in order to be “a being than which none greater can be conceived.” But just because an idea exists in imagination does not necessarily mean that it exists in reality- otherwise there would be many unreal mental objects wandering around. Descartes shares the confusion between conception and existence; a painter’s picture exists in the mind prior to its existence on canvas, but this cannot be true of God, one would assume. In the final analysis, Descartes' proof is based on a mistaken notion that understanding something can ever be a proof of existence. These rational, "good sense" arguments suffer from the same defect: the attempt to use logical or probabilistic tools to explain super-natural reality. They all require the existential “leap of faith.” Strictly speaking, Descartes use of a priori reasoning leads him to a dubious proof of the existence of God. Even the deceiving spirit we mentioned before would also have to be a thinking being, with the idea of a perfect, infinite being-- God. According to Descartes, if the idea of God exists, it is not within the power of the thinker of this idea to diminish or add to it. "No possibility remains, except that this idea is born and produced in me from the moment that I was created, just as was the idea of myself" (p. 49). Certain knowledge of our own existence requires the existence of God, according to this reasoning. The real problem, of course, is that the difference between the Idea of God and the Existence of God, is complete ignored in this reasoning and the definitions upon which it is based. Conclusion In the three different methods of doubt we have looked at in this essay, Descartes does not always keep to his own declared rules for methods, seen in the reduction to doubt vs. self-affirmation in his Discourses. The method itself is laid out clearly in the following series of steps: 1) The first was never to accept anything for true which I did not clearly know to be such... 2) The second, to divide each of the difficulties under examination into as many parts as possible, as might be necessary for its adequate solution 3) The third, to conduct my thoughts in such order that, by commencing with objects the simplest and easiest to know, I might ascend by little and little, and, as it were, step by step, to the knowledge of the more complex... 4) And the last, in every case to make enumerations so complete, and reviews so general, that I might be assured that nothing was omitted. (Descartes, 1969:16-17) These "good sense" procedures involve a good number of definitions and assumptions, however, most important being the assumption of the traditional Aristotelian method of division, classification, and analysis from the simple, single part to the complex, manifold entity that comprises it. Scientific method and common sense both rely on methods of observation, classification and comparison that are not philosophically perfect. In the final analysis, Descartes’ reasoning regarding empirical proofs and metaphysical proofs is not as profound or convincing as his existential, phenomenological “proof” of his own existence: I think, therefore I am. His methods of doubt lead him into a contradiction when he pretends to believe in his own non-existence, but his empirical proofs in physics and a priori proofs of God’s existence do not meet the same standards of pure epistemology.

Bibliography Descartes, Rene. Discourse on Method and The Meditations. New York: Penguin, l968. Descartes, Rene. A Discourse on Method, Meditations and Principles. Translated by John Veitch. New York: Dutton, Everyman, 1969. The Essential Descartes, edited by Margaret D. Wilson, New York: Meridian Books, l969.