RENE DESCARTES 1596-1650

1. RENE DESCARTES1596-1650 • 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. • Hence, early modern philosophy arises coincident with the emergence of natural science as we know it today.

2. Rationalism vs Empiricism • Rationalism asserts that some fundamental knowledge is a priori (Latin: “from the former/prior”), i.e. knowledge independent of sensation and perception • Typically, rationalism maintains that knowledge of universal and necessary truths is a priori • Empiricism, in opposition to Rationalism, asserts that all knowledge is a posteriori (Latin: “from the latter), ie. Knowledge dependent upon sensation or perception.

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’ QUESTIONS • Is the mind different from matter? • Should we adopt the scientific method to advance knowledge? • What can we know with certainty?

5. Descartes’ Substance Dualism • Substance = substrate securing identity of an individual object • Consider pin cushion model • Object = substance (cushion) + attributes (pins) • Cushion remains constant while pins are replaced: substance remains constant while attributes are replaced • Some attributes are essential (irreplacable without destruction of the object) • Others are merely accidental

6. Two Kinds of Substance • Material Substance (Matter): Substrate in an object whose essence is • To be extended in space • Governed by the laws of the physical sciences • Incapable of thinking/feeling • Mental Substance (Mind): Substance in an object whose essence is • To think/feel • To be unextended and not in space • Not governed by the laws of the physical sciences • Dualism: A person = combination of two substances • Is it possible for these two substances to interact?

7. Arguments for Dualism • Conceivability • We can each conceive of ourselves as existing without our bodies • Hence, it is possible for the mind to exist without a body • If it is possible that x exists without y existing, then x is different than y • Hence, the mind and body must be fundamentally different substances

8. Objection • Although may be possible to conceive of x and y as different, this does not imply that x and y must be different things, objects or substances • Eg: It is possible to conceive of Barak Obama as being different from the president. Nevertheless, they are the same. • Thus, even if it is possible to conceive of my mind as being different from my body, they may be the same

9. Argument From Thought and Consciousness for Dualism • The mind is both intentional and conscious • Intentional = represents both what is real and fictious correctly and incorrectly • Conscious = What it is like to think & feel & perceive • Material Substances can’t be intentional or conscious • Hence a mental substance can’t be a material substance

10. Objection • Perhaps material substances are indeed intentional: • Can machines think? • Are computers intelligent? • Are brains thinking things?

11. Descartes as a Foundationalist • Foundationalism: By appropriate use of their rational and perceptual faculties, humans can autonomously come to know with appropriate certainty the fundamental truths of pertaining to both material and mental substances, i.e. discover the true principles of science. This is the basis of all other knowledge • Skepticism • Denies Foundationalism • Asserts that knowledge is impossible because certainty is impossible

12. 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 because of • Evil Demon hypothesis • Hence, certainty is impossible • Hence, knowledge is impossible

13. 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 mental 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.

14. 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. • However, does the example of evil sophomores refute the Cogito?