RENE DESCARTES 1596-1650 French philosopher, mathematician and physical scientist (optics, physics, physiology) 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 A priori knowledge is required in order for there to be a posteriori, empirical or scientific knowledge.

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))

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 certainty the fundamental truths evidentially basic to the empirical or a posteriori sciences of both the world and ourselves

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

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 existence of any particular material substance Dream Hypothesis: hence, no certainty regarding the existence of the material universe generally A priori certainty is impossible because of Evil Demon hypothesis Hence, certainty is impossible Hence, knowledge is impossible

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.

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.

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

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.

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