Chapter 3: Knowledge The Rationalist’s Confidence: Descartes Introducing Philosophy, 10th edition Robert C. Solomon, Kathleen Higgins, and Clancy Martin

Rene Descartes ( ) [AU1: slides contain some duplication of material from one chapter to the next, usually background on a philosopher. For example, some of this material (slides 1-5) on Descartes is also in 2.4a. Will not flag again]French philosopher usually considered the “father of modern philosophy” Raised in the French aristocracy and educated at the Jesuit College of La Fléche Became skilled in the classics, law, and medicine Decided that these fell far short of proper knowledge and so turned to modern science and mathematics

First book was a defense of Copernicus, which he prudently did not publish Discovered, while still young, the connections between algebra and geometry (now “analytic geometry”) Used this as a model for the rest of his career

Basing the principles of philosophy and theology on a similar mathematical basis, Descartes was able to develop a method in philosophy that could be carried through according to individual reason and that no longer depended upon appeal to authorities whose insights and methods were questionable

In Discourse on Method (1637), he set out these basic principles, which he had already used in Meditations on First Philosophy (not published until 1641), to reexamine the foundations of philosophy He sought a basic premise from which, as in a geometrical proof, he could deduce all those principles that could be known with certainty

Galileo raised the doubt that what we think we see we might not really see at all Because of this, Descartes reasons that we could be mistaken in all of our perceptions He begins by doubting all that he knows; once he finds a belief that is indubitable, then he can argue for the truth of other beliefs

The Dream Argument My knowledge of the external world depends upon the evidence of my senses But when I am dreaming, my senses radically mislead me What of mathematical truths? Or other sorts of truths, like extension?

But there could be an evil genius whose only job is to deceive Descartes Could he be deceived about everything?

The one thing that he cannot doubt is the fact of his own existence. If he doubts his existence, he still must exist to doubt it In the second meditation he argues that the evil genius could not possibly fool him about his own thinking. The “I” that he knows to exist is a thinking thing

Descartes uses the premise “I exist as a thinking thing” to prove the existence of God He can think of an infinite, necessary being; therefore, such a being must exist. Once he establishes this, he rebuilds his beliefs on the claim that “God is no deceiver” But he relies on reason to establish the existence of God, and then he claims that God gave him reason to begin with (reason is apparently indubitable). This is called the Cartesian circle

Descartes claims that certain beliefs are self-evident or “clear and distinct” on the basis of intuition and reason alone He believes that there are some kinds of knowledge that we know independent of experience (for example, reason and the claim “I exist”)