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  1. Skepticism

  2. Summary of Last Time Last time we were concerned with the question: “What is knowledge?” We wanted to know what is the essence of knowledge, what it is that makes something knowledge, what is the correct definition of ‘knowledge’.

  3. Three Theories We discussed three theories considered by Socrates and Theaetetus in Plato’s dialogue Theaetetus: • Knowledge = perception • Knowledge = true belief • Knowledge = justified true belief

  4. Knowledge = Perception The main argument that Plato/ Socrates presents against the claim that knowledge = perception is this: There are lots of things that can be known, but which cannot be perceived, like facts about essences, facts about numbers, facts about identity and distinctness. Therefore knowledge cannot be identical to perception.

  5. Knowledge = True Belief Main argument against knowledge = true belief: People often have beliefs based on bad reasons, reasons that don’t support their beliefs at all. So for instance, you might believe that you were going to get in a car accident because a fortune teller told you that you were. Sometimes these beliefs are true “by accident”– but, intuitively, beliefs that are true “by accident” are not knowledge.

  6. Knowledge = Justified True Belief Finally, we considered the most popular account of knowledge for most of the history of Western philosophy: knowledge = justified true belief, a belief that is true, and is believed for good reasons (unlike the fortune teller example). The main objection to this account is similar to the objection to knowledge = true belief.

  7. Accidental Truths Even beliefs that you hold for good reasons, and which are true, can still be “accidentally” true, in the sense that the reason why they are true is totally unrelated to the reasons you have for believing them.

  8. Russell’s Stopped Clock In Russell’s stopped clock case, the fact that the clock says “8:00” is a good reason for believing that it is 8:00AM. And it may be true that it is 8:00AM. But the fact that it is 8:00AM has nothing to do with what the clock says: the clock has stopped, it will say “8:00” no matter what time it is. Even though your reason is a good one, it is only accidental that your belief is true. Intuitively, you don’t know that it’s 8:00AM.

  9. Knowledge First Finally, I introduced the idea that maybe there is no definition of ‘knowledge’ so the project of trying to find one is doomed to failure. This is the “knowledge first” view made popular by Timothy Williamson at Oxford.

  10. Skepticism Today we’re going to set aside the question of what knowledge is and we are going to ask: Is it possible for us to know things? A surprisingly large number of philosophers have answered “NO”– that knowledge is impossible.

  11. Ancient skepticism

  12. SextusEmpiricus (160-210 C.E.)

  13. SextusEmpiricus SextusEmpiricus was a Roman philosopher and physician in the 2nd and 3rd Centuries. The “Empiricus” in his name is from the fact that he belonged to the Empiric school of medicine, which said that medicine should be based on our experiences of what works, and that we should not seek after the hidden, unobservable causes of illness.

  14. SextusEmpiricus In philosophy, Sextus was a follower of a Greek school of thought named Pyrrhonism, after its founder Pyrrho, about whom little is known. Our most complete account of the ideas and arguments of Greek and Roman skepticism comes to us through the writings of Sextus.

  15. Three Views Sextus distinguishes between three views on the question of whether it is possible to know anything: • Dogmatism: knowledge is possible. • Academic Skepticism: knowledge is not possible. • Pyrrhonian Skepticism: I don’t know whether knowledge is possible or not.

  16. Appearances vs. Judgments Sextus makes a distinction between appearances (perceptions, how things look or taste or feel) and judgments (beliefs, how we think things are). The skeptic does not deny appearances– when he feels cold, he will accept that he feels cold– but he refuses to accept any judgment about how things are– that it is cold.

  17. Equipollence The main reason Sextus has for denying Dogmatism and accepting Skepticism is the “equipollence” or “equal force” of arguments on both sides of any issue (except appearances). For any philosophical, logical, mathematical, or scientific claim, you can give equally convincing arguments for and against it.

  18. Observer Effects Sometimes appearances differ from person to person, or between people and animals. For example, a certain temperature might feel cold to you, and fine to me, and hot to a polar bear. How can we say what the world outside of appearances is like, when appearances vary from observer to observer in this way.

  19. Effects of Object’s Condition Sometimes too, the appearances vary, even if they are the same to all observers. For example, snow is white, but snow is water, and water is blue. Or almonds are sweet, but a ground almond is not sweet, but oily. So how can we say how things really are outside of appearances, when they present us with contradictory appearances in different circumstances?

  20. The Historical Argument Another skeptical argument Sextus outlines goes like this: Suppose someone believes a philosophical or scientific view X. Before the view was invented, nobody believed it, they believed something else, Y. So how do you know that some other new view won’t come along and displace X?

  21. The Regress Argument Suppose you have some criterion C for what is true, a way of finding out the truth. If something satisfies the criterion, then it is true, and if something does not satisfy the criterion, it is not true.

  22. The Regress Argument But how can you know that C is such a criterion? You must have some way to tell whether C is a criterion for truth. That is, you must have a criterion C* that tells you “it is true that C is a criterion for truth,” because it has C*.

  23. The Regress Argument C* can’t be identical to C, because it is circular to justify a criterion with itself. (Parody: “How do I know that every sentence less than 20 words long is true? Because the sentence “every sentence less than 20 words is true” is less than 20 words, and therefore true!”)

  24. The Regress Argument Therefore, C* has to be different from C. But how do you know that C* is a criterion for truth? By the same reasoning, there must be some other criterion C** whereby you can tell that “C* is a criterion for truth” is true because it has C**. And there must be a C*** and a C****, and so on, infinitely. But this is impossible.

  25. Two Kinds of Skeptical Argument The first two arguments we considered were “equipollence” arguments. How things look or feel differs “equally” in a way that we can’t say for sure how they objectively are. The historical and regress arguments are noticeably different: you can deny that the evidence on both sides is “equal,” yet still affirm that there’s no reason to believe anything.

  26. The Academy

  27. Academic Skepticism Plato founded the first Western university, the Academy, in Athens. After he died, there was a movement at the Academy toward skepticism. Sextus characterizes Academic Skepticism as the view that nothing is knowable. This was objectionable, because it is insufficiently skeptical: anyone who believes that believes something, but the equipollence of reasons tells you to believe nothing.

  28. Academic Skepticism From what we know, Sextus is probably wrong about what the Academic Skeptics believed: Carneades, the most important of them, thought that you couldn’t know that you couldn’t know anything. Still, the point is a good one: there’s something weird about believing you know that nothing is knowable.

  29. Academic Skepticism The Academics were different from the Pyrrhonian skeptics, however. For example, Carneades held the doctrine of probability: that some things were more probable than others, and you should behave as if the most probable ones were true. This is a denial of equipollence.

  30. Therapeutic Philosophy Last time we learned that Protagoras believed that there was no absolute truth, there was only true-for-you and true-for-me. Therefore, the point of philosophy cannot be to discover the truth or to convince people of the truth– they already have what is true-for-them. Protagoras thought that the goal of philosophy was therapeutic: making people’s lives better.

  31. Skepticism as Therapeutic Skeptics aren’t truth-relativists (they don’t believe truth is relative or that it is absolute, because they don’t believe any philosophical claim). But they cannot hold that the goal of philosophy is to discover the truth, because they don’t believe (or disbelieve) that this is possible. Sextus also says that the goal of skepticism is to improve the lives of the people who believe it.

  32. Ataraxia Sextus tells the story of the famous Greek painter Apelles. According to the story, Apelles was trying to paint a horse’s “foamy saliva,” but kept failing. Angry at his failure, he threw a sponge at the painting and it made a perfect image of foamy saliva. Suddenly, Apelles felt “ataraxia,” an inner quiet and freedom from worry and distress.

  33. Ataraxia What Apelles wanted when he tried, he only got when he had given up. The Pyrrhonians believed that skepticism led to ataraxia. It keeps you from contradictions (remember that equipollence says everything has equal arguments in favor of it), it keeps you from desire (because you don’t believe anything is good), it keeps you from trying to change unavoidable things (because you don’t know how to change them).

  34. Early modern skepticism

  35. Extremely Brief History of the West The history of Western civilization may be divided roughly into the following periods: Classical Antiquity: When Greek and Roman power was at its height. Middle Ages: Catholic dominance. Renaissance: A “rebirth” of art and literature. Modern Period: Science reaches its modern form, discovery of Newton’s Laws, chemistry…

  36. Science Brings Skepticism The Modern Period was a period of scientific change and revolution. The new theories, however, encouraged skepticism, and many early Modern philosophers were faced with the task of deciding what to do about skeptical arguments.

  37. The Historical Argument As new scientific theories replaced old ones, the historical argument for skepticism became more prominent. For example, for the longest time people had believed Galen’s view that the liver and heart both created blood that was then consumed by the rest of the body, until Harvey showed that the heart was a pump and circulated blood throughout the body.

  38. The Historical Argument If what we believed for so long was wrong, people worried, how do we know that Harvey’s theory too will stand the test of time? Perhaps a new theory will come along and unseat it. This was a common Pyrrhic argument, but it was a lot more powerful when revolution was happening all over science.

  39. The Copernican Threat In addition to providing yet another context for the historical argument, Nicolaus Copernicus’ (1473-1543) heliocentrism– the idea that the Earth went around the sun– provoked skepticism in another way. If something as obvious to us as “the earth does not move” is false, then why should we trust other seemingly obvious truths?

  40. The Threat from Atomism Another new scientific theory (one also held by certain Greeks) was the view called atomism: that there were tiny things, atoms, out of which everything else was made. The atoms had shapes, sizes, and they moved around, but they did not have colors, or sounds, or temperature. Color, sound, taste, heat, etc. was all just the effects of atoms moving against our sensory organs.

  41. The Threat from Atomism This certainly suggested skepticism! According to science there were no colors in the world, just in our minds. There was no sweetness, nothing was loud or soft, fire wasn’t hot… everything was atoms and the void. If we are denying that blood is red and snow is white, couldn’t science convince us that anything was false. And if it could, how do we know now what is true?

  42. Michel de Montaigne

  43. Michel de Montaigne Some philosophers became Pyrrhics who rejected the possibility of knowledge (without accepting its impossibility). Michel de Montaigne, perhaps the most famous essayist of the Renaissance, was an advocate of skepticism.

  44. Natural Theology Montaigne had translated a work on Natural Theology by Raymond Sebond. Natural Theology is the idea that you can use reason and evidence to arrive at religious truths, not just the bible. It was of course not a view that the Catholic church liked very much, because it basically questioned the church’s authority to decide the truth.

  45. Montaigne’s Apology The work was put on the list of “banned books” by the church, and so Montaigne wrote an impassioned defense of it “An Apology of Raymond Sebond.” (“Apology” in this context meant “defense,” just as Plato’s “Apology” for Socrates was Socrates’ defense of his views.) But instead of actually defending Sebond’s views, Montaigne defended the idea that since we can’t know anything, we can’t know that Sebondwas wrong!

  46. Skeptical Arguments Mostly, Montaigne just made the same arguments as the ancient skeptics. Here was his version of the infinite regress: Q: Why should we think that fire is hot? A: Because it feels hot. Q: Why should we think that if something feels hot, then it is hot? A: Because when something feels a certain way, it is that way.

  47. Infinite Regress Q: Why should we think that IF it’s true that if something feels a certain way, it is that way THEN it’s true that if something feels hot, then it is hot? …

  48. René Descartes (1596-1650)

  49. Descartes René Descartes was ‘the father of Modern philosophy,’ the first to make a strong break with the earlier Medieval tradition, that was still very oriented toward ancient Greek and Roman thought. We’ve already met Descartes in this class as a defender of substance dualism, the idea that the mind and the body are two different substances.

  50. Descartes’ Project Descartes’ substance dualism was part of a larger project, whereby Descartes thought he could reform all of philosophy, make it compatible with the emerging new science, and establish the principal truths of religion– the existence of God and the immortality of the soul– through reason without recourse to scripture.