In his search for certainty, Descartes found that none of the senses, individually or jointly, provides experience so "clear and distinct" that it is beyond all doubt. Descartes implies that if he could find only one thing that was unquestionably true about his experience, that alone might serve as a foundation for all the other less certain elements of knowledge. With his background it is only natural that he would turn to the intangible precision of mathematics. Still, with his farfetched example of the Evil Genie he shows that it is possible that we could be wrong in our assumptions about mathematics. Perhaps the reason we think we are right in our calculations is simply that we have all learned the wrong way, and continue to teach the wrong way (just as everyone one knew, and taught that the earth was flat, or at the center of the solar system). After all, any hypnotist can make an entire group of people swear a pink elephant is in the room, so why not accept the possibility that mathematics is equally suspect? While mathematics is more reliable and produces more consistent results than sensory knowledge, mathematical knowledge still has that shadow of a doubt.
What can we trust in then? What is always true, even if your thoughts may be controlled by another being? The evil demi-god may make us doubt the existence of our personal belongings, your friends and even our sanity, but he can never make our doubt our own existence. Oh, sure, we might doubt whether we exist in this room, or in this dream, but we cannot doubt that we exist somehow, in some way. The irony is that even if we do doubt, our very activity of doubting proves that we exist. "I think, therefore I am," could equally be expressed as, "I doubt (I am), therefore I am"!
So what good is all of this? What can Descartes possibly do with one piece of indubitable evidence? Quite a bit actually! Itís as though he came to the end of his metaphoric rope, and now he has a good grip with which to start climbing back up. Because this starting point rests in the mind rather than the senses, Descartes is known as a Rationalist.
RATIONALISM is a philosophic orientation to the world that holds knowledge to be based primarily on reason rather than on perception. Rationalists place prime emphasis on thought and deduction rather than on empirical experience and induction.
A belief in rationalism also defines Descartes in a different way, for in separating the rational realm of self awareness, abstract thought and mathematical processes from the experiential realm of sounds colors, textures, tastes and smells, Descartes adopted a Dualistic philosophy.
DUALISM refers to any philosophic view of reality as divided into two fundamental substances, or as understood in terms of two basic realms of being.
That split, in reference to Descartesí dualism, is more commonly referred to as the Mind/Body problem which describes a view in which an immaterial and intellectual dimension is held to be separate from the dimension of oneís physical existence. Descartes held that the rational, intellectual dimension is primary, that is ultimately more reliable since at least one truth derived by the mind is beyond doubt. Descartes then connected the "clear and distinct" truth of reason to the less reliable realm of bodily experience by applying the truths of mathematics and logic to the corporeal realm. But in his "Meditations" he even doubted math and logic by introducing the hypothesis of an Evil Genie who creates our "virtual reality" by constant deception, making us suppose our numbers and measurements are correct, when "Heaven knows what they are adding up to!" Is knowledge of the material realm doomed to doubt? Is there no way for Descartes to "link" us to the everyday world of objects, and indeed, of other bodies?
From the indubitable existence of the self, Descartes did move to knowledge of other beings, only it was not to other human beings. Following a deductive chain of reasoning similar to what follows, Descartes progressed (in the latter "Meditations") from knowledge of self, to knowledge of God, and ultimately to the validation of mathematics and logic, the instruments for measuring and predicting the material world. Descartes reasoned that:
With our own existence assured, and too, by direct implication, Godís existence, Descartes has a firm basis for re-instating the credibility of mathematics. Why? Because God, who is all-good, "is no deceiver". Maybe some Evil Genie would trick us into perpetually making the wrong mathematical calculation, but God is not so malicious. Thus, 7 + 3 most certainly does equal 10. Once we have regained the validity of numerical measurement, science has the key for describing the "other" half of reality, the physical dimensionÖ so Descartes really has "saved the world"!