Descartes' Philosophy: Methodical Doubt and Existence

Theory of Knowledge

In The Discourse on Method (1637), Descartes summarizes the rules of method for attaining true knowledge in these four:

1. Do not accept as true anything that is not presented so clearly and distinctly that it does not fit doubt.
2. Divide the problems up to the simple natures.
3. Drive thoughts in order, going from the most simple to the more complex.
4. Make enumerations so complete and reviews so general that you can be sure not to forget anything.

It is, therefore, necessary to remove (considered as false) everything that is possible to doubt. In the Meditations, we can distinguish three levels of subsequent radicalization of methodical doubt:

1. He doubts that things are as they seem according to the testimony of the senses, as these have sometimes deceived him.
2. He doubts even that there are things that he perceives, as they may be merely a dream, due to the inability to distinguish waking from sleep.
3. He doubts even mathematical truths (which would apply even in dreams) as he raises the hypothesis that a "God deceiver" or better, an "evil genius" would have made us so that we are deceived whenever we believe we are in truth.

It seems that he cannot save any truth but this: as much as the evil genius fools me, if I am fooled, I fool someone; if I am fooled, I am. "Doubt" and "Deception" are forms of "thinking." Hence his famous formulation: "I think, therefore I am." It follows that Descartes' criterion of certainty is: whatever is perceived with equal clarity and distinction will be true. He has saved the existence of the self as a thinking subject, but how to avoid solipsism? Descartes will have to try to deduce the existence of the world from the existence of thought. As to its content, we can distinguish:

• Adventitious ideas: Those that appear to come from foreign experience.
• Factitious ideas: Those that the mind constructs from other ideas.
• Innate ideas: These are the most important and from which he has to build the edifice of our knowledge.

Metaphysics

To meet the third level of doubt and to recover the outside world, Descartes must first prove the existence of God (which, being omnipotent and infinitely good, would not have created us to deceive us or take pleasure in believing to be true). He proposes three tests, the three parts of the idea of God:

1. From our innate ideas is the idea of perfection or infinity. I cannot be the cause of this idea because there must be at least as much perfection in the cause as in the effect. I know that I am imperfect, therefore that idea had to be caused in us by a perfect being, God (1^st test).
2. Whoever knows something more perfect than himself cannot be himself; he has had to receive his contingent being from whoever has given him the idea of perfection, of God (2^nd test).
3. The idea of God is that of being absolutely perfect, but existence is a perfection, therefore God exists (3^rd test).

Since God exists and is infinitely good and true, he cannot let me fool myself into believing that the world exists. As before Galileo, he denies that there are secondary qualities (colors, sounds, etc.). God only ensures the existence of a world constituted by extension, which is the essence of bodies, and movement (primary quality, the basis of mechanistic physics, governed by the principle of conservation of motion and the principle of inertia). Descartes distinguishes three levels of reality: God or infinite substance, the self or thinking substance, and bodies or extensive substance. In Principles I, 51, he defines substance as that which does not need anything else to exist. He recognizes that this definition can only be applied absolutely to God, but also holds for finite beings due to their mutual independence.