RENE DESCARTES 1596-1650

1. RENE DESCARTES1596-1650 • French philosopher, mathematician and physical scientist (optics, physics, physiology) • Catholic • Initially educated at the Jesuit college of La Fleche • Then at the University of Poitiers • Lives in the immediate aftermath of the Protestant Reformation initiated by Martin Luther (1483-1546)

2. RENE DESCARTES • Father of Early Modern Rationalist Philosophy • Early Modern Philosophy is characterized by the thesis that genuine knowledge can be achieved by humans through the use of their rational and perceptual faculties independent of any form of divine revelation. • A priori knowledge is possible and deploys innate “clear and distinct ideas” • A priori knowledge is required in order for there to be a posteriori, empirical or scientific knowledge.

3. Descartes’ Scientific Contemporaries • Copernicus (Polish; 1473-1543) • Astronomy: Heliocentric solar system • Challenge to Church-endorsed Geocentric universe • Francis Bacon (English; 1561-1626) • Development of the scientific method • Galileo (Italian; 1564-1642) • Mathematician, Physicist & Astronomer; Copernican • Challenge to Church’s claims of divine revelation of natural laws • Kepler (German; 1571-1630) • Discovered laws of planetary motion • Boyle (Irish; 1627-1691) • Developed experimental chemistry; worked in mechanics, medicine, hydrodynamics • Newton (English; 1642-1727) • Fundamental laws of physics; classical mechanics • Develops the calculus (independently, so too does Leibniz (1646–1716))

4. Descartes as a Foundationalist • Descartes is a Foundationalist who repudiates the Augustinian doctrine of Illumination and affirms that the human mind is capable of genuine knowledge of universal and necessary truths • Foundationalism: By appropriate use of their rational faculties for a priori reasoning, humans can autonomously come to know with appropriate certaintythe fundamental truths evidentially basic to the empirical or a posteriori sciences of both the world and ourselves

5. Descartes’ Refutation of Skepticism • As a Foundationalist, Descartes refutes Skepticism • The skeptic maintains that • Certainty is required for knowledge • However, humans are incapable of certainty • Hence, humans are incapable of knowledge • Thus, science of both the world and ourselves is impossible

6. The Skeptic’s Argument • Meditation I: Descartes’ provisional argument on behalf of the skeptic • Knowledge requires certainty. • Certainly is either empirical or a priori • Empirical certainty is impossible because of • Illusion: hence, no empirical certainty regarding attributes of material substances • Hallucination : hence, no certainty regarding the qualities of of any particular material substance • Dream Hypothesis: hence, no certainty regarding the existence of either any particular material substance or material universe generally • A priori certainty is impossible because of • Evil Demon hypothesis • Hence, certainty is impossible • Hence, knowledge is impossible

7. The Cogito as Descartes’ Reply to the Skeptic • Cogito, ergo sum! • No evil demon could delude one about one’s own existence • Thus, some a priori knowledge is possible! • Each person can be a priori certain and have genuine a priori knowledge about • His/her own individual existence as a thinking substance • The existence and content of his/her own current ideas (i.e. psychological or mental attributes). • Thus, one can know with a priori certainty what one believes about • God • The material universe.

8. From the Cogito, through the Ontological Argument, to A Priori Knowledge • Thus, one may know with certainty the content of one’s idea of God as the perfect being. • Thus, Anselm’s Ontological Argument is certain and sound. • Hence, God exists! • God’s existence implies that the Demon Hypothesis is false. • Hence, a priori reasoning can provide certainty. • Hence a priori knowledge of all of logic and mathematics is possible.

9. Empirical Knowledge is Possible Too • Perceptual ideas are known reflections within the mind of the (yet) unknown character and existence of the external material • The existence of God implies that sensation and perception – if employed according to God’s design and as characterized by science - produce generally reliable, even if not absolutely certain, representations of the material universe. • Hence, empirical knowledge of the material universe is possible through science

10. Problems with the Cogito as the Foundation of Knowledge • Circularity in arguments for the existence of God in refuting the Demon Hypothesis • Descartes appeals to the Ontological Argument to refute the Demon Hypothesis. • But, the Ontological Argument is an instance of a priori reasoning. • All a priori reasoning is dubious according to the skeptic’s evil demon hypothesis • So, the Ontological Argument circularly presupposes that the evil demon hypothesis is false • In that case, the Ontological Argument is not a legitimate refutation of the evil demon hypothesis.

11. Other Problems with the Cogito • The Cogito aims to demonstrate that we know with certainty our current thoughts. • But empirical evidence suggests the opposite: • Evil Sophomores and the effects of psychological priming: • I might falsely believe that I am experiencing pain • The unattended channel and confabulation