1. Rene Descartes 1596—1650

2. Some dates 1543: publication of Copernicus’s De Revolutionibus 1543: publication of Copernicus’s De Revolutionibus 1633: Galileo arrested 1633: Galileo arrested 1641: publication of the Meditations 1641: publication of the Meditations

3. Some reasons to doubt the senses Past error Past error Insanity/delusion Insanity/delusion Dreams Dreams Possibility of demon/evil genius/malicious god Possibility of demon/evil genius/malicious god

4. How do these lead us to doubt the senses? 1. All our knowledge of the external world is based on sense experience 2. Unless I have a reason to think my sense experience is reliable, I have no reason to believe in an external world 3. I can’t have any reason to think my senses are reliable 4. Therefore, I have no reason to believe in an external world

5. What can I know?

6. I think; therefore I am!

7. What am I?

8. Plato: (428-347BCE) I am a featherless biped

9. Aristotle: (384-322BCE) I am a rational animal

10. I am a thinking thing! Descartes:

11. Personal Identity What am I?

12. Descartes: I am my mind I am essentially rational, only accidentally an animal I am essentially rational, only accidentally an animal The demon thought experiment indicates that I could exist even if my body did not, so I am not my body The demon thought experiment indicates that I could exist even if my body did not, so I am not my body

13. Metaphysics and Epistemology Metaphysics: the study of what there is, the fundamental nature of reality Metaphysics: the study of what there is, the fundamental nature of reality Epistemology: theory of knowledge and justified belief, reason, evidence, etc. Epistemology: theory of knowledge and justified belief, reason, evidence, etc.

14. Rationalism All or most of our knowledge is a priori, i.e., knowable independently of experience, i.e., on the basis of pure reason All or most of our knowledge is a priori, i.e., knowable independently of experience, i.e., on the basis of pure reason Epistemological view Epistemological view All or most of our concepts are innate All or most of our concepts are innate Psychological view (aka nativism) Psychological view (aka nativism)

15. Empiricism All or most of our knowledge is a posteriori, i.e., knowable only on the basis of experience All or most of our knowledge is a posteriori, i.e., knowable only on the basis of experience Epistemological view Epistemological view All or most of our concepts are learned All or most of our concepts are learned Psychological view (sometimes called “concept empiricism”) Psychological view (sometimes called “concept empiricism”)

18. Descartes’s skepticism Gives us reason to doubt the senses Gives us reason to doubt the senses Highlights distinction between appearance and reality Highlights distinction between appearance and reality

19. 1. Nothing is ever directly present to the mind except its own ideas (e.g., sense experiences) 2. To know anything about the external world, I would first have to know these ideas accurately represent the external world 3. But I couldn’t have any non-question-begging reason for believing that, thus can’t know it 4. Therefore, I can’t know anything about the external world

20. 1. Nothing is ever directly present to the mind except its own ideas (e.g., sense experiences) 2. To know anything about the external world, I would first have to know these ideas accurately represent the external world 3. But I couldn’t have any non-question-begging reason for believing that, thus can’t know it 4. Therefore, I can’t know anything about the external world

21. If I can come up with an a priori argument for the reliability of sense-perception, it won’t be question-begging

22. I think; therefore I am!

23. What do I know? That I think That I think That I exist That I exist That I’m thinking about …. That I’m thinking about …. E.g., that I’m in pain (understood as purely mental), that I’m having a visual experience as of a desk, etc. E.g., that I’m in pain (understood as purely mental), that I’m having a visual experience as of a desk, etc. That I am a thinking thing (that I am my mind) That I am a thinking thing (that I am my mind)

24. Mind is better known than body, even though bodies are perceptible, minds are not Surprising, if we confuse understanding with imagining

25. Imagination: capacity for forming sensory images of things (e.g., seeing “in the mind’s eye”) Imagination: capacity for forming sensory images of things (e.g., seeing “in the mind’s eye”) Understanding: capacity for pure, nonsensory thought Understanding: capacity for pure, nonsensory thought

26. triangle (-2, -4), (3, 7), (1, -5)

27. Not all knowledge involves imagination Not all knowledge involves imagination (In fact, none does) (In fact, none does) Why does imagination have such a grip on us? Why does imagination have such a grip on us? Because it gives us clear---though not distinct---ideas Because it gives us clear---though not distinct---ideas Clear: accessible to the attentive mind (opposed to obscure) Clear: accessible to the attentive mind (opposed to obscure) Distinct: sharply separated from other ideas (opposed to confused) Distinct: sharply separated from other ideas (opposed to confused)

28. Wax example Piece of wax has a certain taste, odor, size, color, shape, texture, solidity, sound. Bring it near a heat source and all of these change. Still we know that it is the same piece of wax. Our knowledge of the wax is not through the senses but through the intellect alone. To perceive the wax is not strictly to see it, but to understand it The wax itself is an invisible substance that has perceptible properties. We can’t imagine the wax itself, though we can understand it

29. What do I know? That I know that I think That I know that I think That I know that I exist That I know that I exist So I know something about knowledge What does my perception of my own existence have that qualifies it for being knowledge? That I clearly and distinctly perceive it to be true Therefore, whatever I clearly and distinctly perceive to be true, really is true

30. Clarity and Distinctness Principle Whatever I clearly and distinctly perceive to be true, really is true Can we give a more rigorous proof? 1. God exists. 2. God wouldn’t let me be deceived when I’m doing my very best to avoid error 3. The best I can do is assent to only what I clearly and distinctly perceive to be true 4. Therefore, whatever I clearly and distinctly perceive to be true, really is true

31. Argument for God’s Existence--- Background Formal reality/existence: existence in fact, real existence Formal reality/existence: existence in fact, real existence Objective reality/existence: existence in thought Objective reality/existence: existence in thought

32. Argument for God’s Existence: Causal principles known a priori Everything has a cause. Some corollaries: There must be at least as much reality in the cause as in the effect. There must be at least as much reality in the cause as in the effect. (otherwise, part of the effect would be uncaused) (otherwise, part of the effect would be uncaused) There must be at least as much formal reality in the cause as there is objective reality in the effect There must be at least as much formal reality in the cause as there is objective reality in the effect (all causes must have formal reality) (all causes must have formal reality)

33. Argument for God’s Existence: 1. I have an idea of God, i.e., an infinite being 2. This idea has infinite objective reality 3. There is as at least as much formal reality in the cause as objective reality in the effect 4. Therefore, this idea is caused by a thing with infinite formal reality 5. Therefore, an infinite thing exists 6. I.e., God exists

34. Argument for reliability of cognitive faculties: 1. God (exists and) is infinite (from earlier argument) 2. Therefore, God is perfect (from 1) 3. To deceive is to be lacking in some perfection 4. Therefore, God is not a deceiver (2, 3) 5. God is (directly or indirectly) responsible for my existence 6. If God allowed me to be mistaken, even when I’m doing my very best to avoid error, he would be a deceiver (5) 7. Since he’s not a deceiver (4), it must be that when I’m doing my very best, I can’t go wrong (4, 6) 8. The best I can do is to assent to only what I clearly and distinctly perceive to be true 9. Therefore, what I clearly and distinctly perceive to be true really is true (Clarity and Distinctness Principle)

35. Problem: how is it that we ever err? By not using judgment properly Judgment is really result of two faculties: Intellect: perceives ideas Intellect: perceives ideas Will: chooses what to believe Will: chooses what to believe Intellect is finite, will is infinite Since the will extends farther than the intellect, it is possible to believe what we don’t perceive to be true. Since the will extends farther than the intellect, it is possible to believe what we don’t perceive to be true.

36. The essence of material things Clear and distinct ideas of extension (taking up space), motion, duration Innate knowledge of numbers figures, movements, etc. Innate knowledge of numbers figures, movements, etc. The principles of geometry are clear and distinct, thus knowable. The principles of geometry are clear and distinct, thus knowable. Mathematics in general more certain than belief based on sensation Mathematics in general more certain than belief based on sensation

37. Descartes’s epistemology Intuition: self-evident knowledge; knowledge that does not depend on other knowledge (basic beliefs) Demonstration: knowledge that does depend on other knowledge (nonbasic beliefs) Foundationalism: some beliefs are basic (noninferentially justified, foundational); and all other justified beliefs ultimately derive their justification from inferential connections to basic beliefs

38. Proof: string together intuitions, so that each step in the proof is self-evident, can render something clear and distinct that wasn’t previously Clarity and distinctness goes away over time, becomes possible to doubt Clarity and distinctness goes away over time, becomes possible to doubt Existence of God, fact that he is no deceiver, ensures that what is – or was once – clearly and distinctly perceived is true Existence of God, fact that he is no deceiver, ensures that what is – or was once – clearly and distinctly perceived is true Knowledge of God’s existence essential for perfect knowledge on the basis of proof Knowledge of God’s existence essential for perfect knowledge on the basis of proof

39. The Cartesian Circle Famous objection to Descartes’ project in Meditations: Descartes assumes at beginning of 3rd Meditation that what is clearly and distinctly perceived is true Descartes assumes at beginning of 3rd Meditation that what is clearly and distinctly perceived is true Uses this to prove God’s existence Uses this to prove God’s existence Uses this to prove that what is clearly and distinctly perceived is true. Uses this to prove that what is clearly and distinctly perceived is true. Problem: there’s a vicious circularity here: can’t know that God exists unless we already know that what we clearly and distinctly perceive is true

40. Partial solution? In proofs, clarity and distinctness goes away over time, becomes possible to doubt In proofs, clarity and distinctness goes away over time, becomes possible to doubt Existence of God, fact that he is no deceiver, ensures that what is – or was once – clearly and distinctly perceived is true Existence of God, fact that he is no deceiver, ensures that what is – or was once – clearly and distinctly perceived is true Knowledge of God’s existence essential for “perfect knowledge” on the basis of remembered proof Knowledge of God’s existence essential for “perfect knowledge” on the basis of remembered proof Atheist geometer can have a sort of knowledge, but not the unshakeable knowledge that a theist can have

41. Return of the External World: I. My Own Body Recall imagination/understanding distinction Probabilistic argument for the existence of body 1. I could exist/endure without capacity for imagination 2. Therefore, the imagination depends on something distinct from me 3. A body conjoined to me could be the means by which I imagine things 4. No other candidates seem very likely 5. Therefore, I probably have a body

42. Return of the External World: II. Other Bodies 1. The capacity for sensing that is in me is passive (I don’t choose to create ideas of sensation) 2. I’m not the cause of my ideas of sense – they’re typically involuntary 3. There must be some source of these ideas, outside of me 4. If the real cause is anything other than the bodies the ideas are of, then God is a deceiver. 5. God is not a deceiver, so there must be bodies

43. Return of the External World: III. The Nature of Bodies Sensation only tells me that there are bodies, gives me clear and distinct ideas of bodies as objects of mathematics. Anything else I believe is my choice, not God’s doing Anything else I believe is my choice, not God’s doing “Bodies as objects of mathematics” i.e., bodies insofar as they have a particular shape, size, motion, solidity, etc. i.e., bodies insofar as they have a particular shape, size, motion, solidity, etc. “Primary Qualities” “Primary Qualities” But not insofar as they have particular taste, odor, color, sound, etc. But not insofar as they have particular taste, odor, color, sound, etc. “Secondary Qualities” “Secondary Qualities”