Descartes’ Radical Doubt

1. Descartes’ Radical Doubt

2. Blank Slate vs. Hard Wired When we come into the world at birth, the mind is like a blank tablet. Or Some ideas are directly known by the mind and are not learned from experience: a. the laws of logic; b. the basic principles of mathematics; c. cause/effect; d. concept of perfection; e. idea of God; f. moral concepts.

3. Knowledge, Probability, and Certainty Our knowledge of reality can never be absolutely certain. However, if a belief is true and we have sufficient evidence of its probability, we have knowledge. or Through reason, it is possible to have knowledge about reality that is absolutely certain.

4. Is the Problem of Knowledge Really a Problem? If we are born “blank slates,” what obligations do we have to ensure that all have equal opportunity to gain knowledge? If knowledge about the nature of reality is primarily a priori, how should children be educated? If nothing can ever be known, how can anything ever be condemned, celebrated, or communicated? If certainty is impossible, by what criteria do we claim that a belief is justified?

5. God and Religion 1= I do have knowledge. 2 =Knowledge is possible but I don’t know the answer. 3=Knowledge is impossible. There is a God. Supernatural miracles do not occur. There is life after death. One particular religion is the true one. 4-6=very confident 10-12=very skeptical

6. Science 1= I do have knowledge. 2 = Knowledge is possible but I don’t know the answer. 3=Knowledge is impossible. Science gives us the best information about reality. Science can tell us about the origins of the universe. Science can tell us about the origins of human life. Scientists will one day be able to explain all human behavior. 4-6=very confident 10-12=very skeptical

7. Moral Knowledge 1= I do have knowledge. 2 = Knowledge is possible but I don’t know the answer. 3=Knowledge is impossible. Some actions are objectively right or wrong. The convention of one’s society determine what is right or wrong. Pleasure is the only thing in life that has value. Sometimes it could be one’s moral duty to lie. 4-6=very confident 10-12=very skeptical

8. Skepticism Sense organs are unreliable. Sense data is not the thing. We cannot get outside of our minds or experiences to verify that what we claim is true is, in fact, true. We “know” only our individual thoughts (which is really to say that we think). Universal skeptics: no one knows anything. Limited skeptics: some claims to knowledge are doubtful. You claim to know what????

9. Strategies of the Skeptic Universal Belief Falsifiers It is theoretically possible that X [I’m a figment of your imagination, you’re a brain in a vat, our eyes distort images of the material world, we’re in the matrix, you’re dreaming, etc.]. If X were the case, we would have no way of knowing it. Since we have no way of knowing whether X is the case or not, we cannot know whether claims related to or dependent upon X are true or false. Therefore, we have no knowledge.

10. Another Strategy of the Skeptic You claim to know, so prove it. And while your at it, tell me why my arguments for doubt are wrong. If you have no fail-safe method for establishing whether something is true or false, then you have no justification for claiming to know that something is true or false.

11. Generic Skeptical Argument • We can find reasons for doubting any one of our beliefs. • It follows that we can doubt all our beliefs. • If we can doubt all our beliefs, then we cannot be certain of any of them. • If we do not have certainty about any of our beliefs, then we do not have knowledge. 5. Therefore, we do not have knowledge.

12. Descartes’ Method “Some years ago I was struck by the large number of falsehoods that I had accepted as true in my childhood, and by the highly doubtful nature of the whole edifice that I had subsequently based on them.” Examples of falsehoods?

13. Radical Doubt “Reason now leads me to think that I should hold back my assent from opinions which are not completely certain and indubitable just as carefully as I do from those which are patently false. So, for the purpose of rejecting all my opinions, it will be enough if I find in each of them at least some reason for doubt.” Possible doubt=uncertain. Senses deceive. Therefore, “knowledge” based on sense experience is rejected.

14. “How could it be denied that these hands or this whole body are mine? “I see plainly that there are never any sure signs by means of which being awake can be distinguished from being asleep.”

15. Anything I think I know that is based on my sensory experiences or my experience of my body is suspect. I am not certain there is a world “out there,” and I am not certain I have a body. What’s left?

16. Trying Out the Skeptical Argument Lemons are yellow. The moon is much farther away from me than the tops of the trees are. I am (X) years old. American astronauts have visited the moon. I am now reading this PowerPoint slide. This room is filled with light.

17. Mathematics 2+3=5 Or does it?

18. There’s no world out there, I have no body, and I can’t trust my thoughts. A deceiver implies a deceived. Doubt requires a doubter. Thought requires a thinker. I think; I exist.

19. Ones’ essence—i.e. self—is non-material (mind, soul). The fundamental activity of this self is thinking, doubting, wondering, etc.

20. Life as a Brain in a Vat is Really Not Much of a Life So how can Descartes reclaim the world? Must find God. If there is an all-powerful, all-knowing, all-good God, then there the evil genius cannot be calling all the shots. And God must be found in a priori knowledge.

21. Some Questions Does skepticism/doubt promote tolerance or does it give license to anti-social behavior? Is it possible to live our lives without the psychological comfort of certainty? Assuming the skeptics are right that genuine knowledge is impossible, can they still claim that some beliefs are more worthy of being embraced than others? Is it better to live in ignorant certainty or in thoughtful doubt? When does skepticism become a cop out—that is, an easy way to avoid defending a claim? To what degree should we trust our senses? Is skepticism livable?