Descartes’ Theory of Reality: Dualism and Certainty in Philosophy

1. Lecture 6: Descartes

2. Lecture Outline • In today’s lecture we will: • Become introduced to Rene Descartes • Begin our investigation into Descartes’ theory of reality • Examine Descartes’ philosophical aims and method • Outline and critically consider Descartes’ arguments for: • The existence of mental substances • The existence of God • The existence of physical substances • Discuss the validity of Descartes arguments

3. Descartes’ Theory of Reality

4. Descartes’ theory of reality Rene Descartes Lived 1596 – 1650 Another important figure in the history of philosophy Discovered analytic geometry A pioneer of scientific discovery and the enlightenment Possessed his own distinct philosophical method Endorsed a Dualist theory of reality (Substance Dualism)

5. Descartes’ theory of reality • Substance Dualism (a prelude) • Descartes argues that reality is composed of Two distinct Substances: • Physical Substances • Mental Substances

6. Descartes’ theory of reality Why should we carve reality up into two substances? Problem 1 (P1) Our senses can (and often do) deceive us So how can we trust any of our senses? Which line is longest?

7. Descartes’ theory of reality Why should we carve reality up into two substances? Problem 2 (P2) Traditional philosophy (before science) can only give us possible answers Nothing in philosophy is beyond dispute and nothing is certain Q: Why does fire/heat always go upwards? Aristotle: Its essence is heavenly and when released it tries to return back to its native essence.

8. Descartes’ theory of reality • Why should we carve reality up into two substances? • Overall problem: • Existing philosophical theories and our senses are unable to give us Certain Knowledge • Certain knowledge is to be preferred over uncertain knowledge • Unless philosophy can arrive at certain knowledge its future is in doubt • Descartes’ aim: • Descartes sought to build a new philosophy that: • Arrived at certain knowledge • Gave answers that were beyond dispute

9. Descartes’ theory of reality The search for certainty Mathematics do provide us with certain knowledge: Mathematical knowledge is not derived from the senses Mathematical knowledge is beyond dispute Its truth can be demonstrated 2+2=4 Mathematical truths are discovered through Reason Alone

10. Descartes’ theory of reality • The birth of modern philosophy • Descartes attempted to apply the mathematical method (using reason alone) to philosophy • He attempted to use reason alone to find one thing which is absolutely certain (beyond doubt, beyond dispute, not derived from the senses) • The criterion of such knowledge is Clarity and Distinctness • Once found, Descartes hoped to use intuition and deduction to find further certainty. • To find this one certainty Descartes tries proceeds by employing systematic (Cartesian) doubt

11. Descartes’ theory of reality Cartesian Doubt Descartes attempts to doubt everything that can be doubted If there is any possibility of doubting something, it is insufficient Descartes’ goal is to find a truth which is beyond doubt. On what grounds might we doubt the following: “This is my right hand, it has five fingers” “The Earth revolves around the sun” “I am teaching Phi-100 at DCCC” “I like the taste of ice cream” “The person teaching Phi-100 at DCCC exists” “The person teaching Phi-100 is human”

12. Descartes Arguments for Substance Dualism

13. Descartes’ theory of reality I – The Existence of Mental Substance Descartes discovered that the one thing beyond all doubt is: “I think therefore I am” (Cogito Ergo Sum) 1. It is certain that I exist Even if I am being deceived about my own existence then there is still something (myself) being deceived 2. I am a mind or a thing that thinks To be able to doubt I must be thinkingDoubting that I am thinking is contrary to reason and logic! Therefore: We can be certain that mind exists We can also be certain that Mental Substance exists

14. Descartes’ theory of reality • II – The Existence of God • Descartes uses his ‘First Principle’ to deduce two arguments for God’s existence • 1. The Eidological argument • Q: Where does the idea of perfection (or God) come from? • It cannot come from experience or the senses • Cannot come from nowhere • I cannot merely invent the idea of perfection • Therefore: • A1: The only rational answer is that the idea of perfection was placed in our minds by God • A2: God exists

15. Descartes’ theory of reality II – The Existence of God Descartes uses his ‘First Principle’ to deduce two arguments for God’s existence 2. The Ontological argument God, by definition, is that being which is absolutely perfect It is more perfect to exist than not to exist Therefore, to conceive of God it is necessarily to conceive of him as existing Therefore, to say “God does not exist” is to contradict oneself Therefore, the sentence “God exists” is necessarily true Therefore: We can be certain that God exists

16. Descartes’ theory of reality • III – The Existence of Physical Substance • We can doubt the existence of the world and external objects because: • We might be dreaming • A demon might be deceiving us (similar to The Matrix) • But! God is incapable of deceiving us • All judgements that have clarity and distinctness come from God • All true or certain knowledge depends on God • Any errors in judgement or knowledge come from human error and not God • Observations: • We cannot choosewhether to experience an external world • We receive impressions from things outside of us passively • Therefore Physical Substance Exists • (But only because of God)

17. Descartes theory of Reality

18. Descartes’ theory of reality Descartes’ Theory of Reality (Reprise) We can be certain that reality is composed of two distinct substances Physical and Mental Substances Each substance exhibits the following properties: