So, among your current vast store of indubitable beliefs are the following: It seems to me that I am in Philosophy 100.

Transcription

1 From last time By following the method of doubt by discarding every belief that could possibly be false Descartes has eliminated every statement about the nature of the physical world. While that eliminates a huge number of our ordinary beliefs, it does still leave us with a large set of indubitable premises. That set includes every statement you can think of about how the world seems to you not how you think the world actually is, but only how it seems to you at this moment. Because while you could be wrong about any of your beliefs about the nature of the world, given the existence of an Evil Genius (or if you are a brain in a vat), you cannot be wrong about how is seems to you right now. 1

2 So, among your current vast store of indubitable beliefs are the following: It seems to me that I am in Philosophy 100. So, among your current vast store of indubitable beliefs are the following: It seems to me that I am in Philosophy 100. It seems to me that I have a body. 2

3 So, among your current vast store of indubitable beliefs are the following: It seems to me that I am in Philosophy 100. It seems to me that I have a body. It seems to me that my name is (fill in the blank). So, among your current vast store of indubitable beliefs are the following: It seems to me that I am in Philosophy 100. It seems to me that I have a body. It seems to me that my name is (fill in the blank). It seems to me that I am thirsty. 3

4 So, among your current vast store of indubitable beliefs are the following: It seems to me that I am in Philosophy 100. It seems to me that I have a body. It seems to me that my name is (fill in the blank). It seems to me that I have heard this part of the story before in the last lecture. So it may be false that: You are in Philosophy 100. You have a body. Your name is (fill in the blank). You have heard this part of the lecture before. But no one can disprove or cast doubt on the fact that this is how it seems. Of this you are CERTAIN. 4

5 A VERY LARGE PROBLEM If you have knowledge of only how the world seems to you, then you have knowledge of only the contents of your own thoughts. But starting from this basis this set of axioms how will you ever gain knowledge about the world beyond you, about what is the case beyond your own thoughts, about the basic facts about the world? Descartes himself realized that he had backed himself into a philosophical corner. Take ANY statement about how the world seems to you. No matter what statement you pick, given Descartes method of doubt, it is always possible that the world is not how it seems. So given the axioms plus the rules of logic alone, you cannot prove anything about the external world. 5

6 THE RESULT: Skepticism about the nature of the external world. Without adding any more axioms, we seem to have skepticism about the external world (I.e. there is nothing we can know about). As this is hardly what Descartes had hoped to achieve, Descartes attempts to find a way out. Descartes Answer: A Benevolent God 6

7 1. We find in each adult, an idea of an all good, all powerful, and all knowing God. 1. We find in each adult, an idea of an all good, all powerful, and all knowing God. 2. From this idea of God alone, we can prove that there is a God (of this kind). (There is no other way we could have come to have an idea of an all good God, unless God himself has given us this idea.) 7

8 1. We find in each adult, an idea of an all good, all powerful, and all knowing God. 2. From this idea of God alone, we can prove that there is a God (of this kind). (There is no other way we could have come to have an idea of an all good God, unless God himself has given us this idea.) 3. Because God is both all benevolent and all powerful, he would not have created a creature, humankind, in a way that meant we would be systematically decieved. (God is not a evil genius.) 1. We find in each adult, an idea of an all good, all powerful, and all knowing God. 2. From this idea of God alone, we can prove that there is a God (of this kind). (There is no other way we could have come to have an idea of an all good God, unless God himself has given us this idea.) 3. Because God is both all benevolent and all powerful, he would not have created a creature, humankind, in a way that meant we would be systematically decieved. (God is not a evil genius.) 4. Therefore, God must have created mankind such that, if we use our rational faculties correctly, we can tell which of our beliefs about the external world are false and which are true. 8

9 1. We find in each adult, an idea of an all good, all powerful, and all knowing God. 2. From this idea of God alone, we can prove that there is a God (of this kind). (There is no other way we could have come to have an idea of an all good God, unless God himself has given us this idea.) 3. Because God is both all benevolent and all powerful, he would not have created a creature, humankind, in a way that meant we would be systematically decieved. (God is not a evil genius.) 4. Therefore, God must have created mankind such that, if we use our rational faculties correctly, we can tell which of our beliefs about the external world are false and which are true. 5. We can have knowledge (certain knowledge) about the world. Where does one go from here? 1. Either our justification for our beliefs must be certain or our justification can be less than certain. 2. If we accept that knowledge must be certain, then the only knowledge we have is about the contents of our own thoughts. 3. Surely we have knowledge about more than the contents of our thoughts. 4. So we can know certain facts without having indefeasible evidence for them (with less than certain justification.) 9

10 Locke Practically speaking, there are two ways in which we can know when our perceptual beliefs about the world are true: A. When they come to us involuntarily. Certain of our thoughts we can bring to mind voluntarily. E.g. I can think about the Tower of London or Big Ben or The Taj Mahal and have a reasonably good image of them in my mind. But other visual experiences are forced upon me : if my eyes are open, I HAVE to see whatever is before me. Locke Practically speaking, there are two ways in which we can know when our perceptual beliefs about the world are true: A. When they come to us involuntarily. Certain of our thoughts we can bring to mind voluntarily. E.g. I can think about the Tower of London or Big Ben or The Taj Mahal and have a reasonably good image of them in my mind. But other visual experiences are forced upon me : if my eyes are open, I HAVE to see whatever is before me. B. When those experiences are consistent (both with our other experiences and with the experiences of others.). 10

11 While this tactic might seem practical and seems that it would work to sort out, for the most part true from false beliefs in every day life, it has a bizarre consequence for any theory of knowledge. IT MAKE IT POSSIBLE TO HAVE KNOWLEDGE ABOUT THAT WHICH IS NOT THE CASE. Consider the case of the brain in the vat again. 11

12 Consider the case of the brain in the vat again. 1. If you are a brain in a vat, then your experience is just as involuntary as it would be if you were NOT a brain in a vat. Consider the case of the brain in the vat again. 1. If you are a brain in a vat, then your experience is just as involuntary as it would be if you were NOT a brain in a vat. 2. If you are brain in a vat, your experience is just as consistent as it would be if you were NOT a brain in a vat. 12

13 Consider the case of the brain in the vat again. 1. If you are a brain in a vat, then your experience is just as involuntary as it would be if you were NOT a brain in a vat. 2. If you are brain in a vat, your experience is just as consistent as it would be if you were NOT a brain in a vat. 3. Therefore, your conclusions about the external world are equally justified whether or not you are a brain in vat. Consider the case of the brain in the vat again. 1. If you are a brain in a vat, then your experience is just as involuntary as it would be if you were NOT a brain in a vat. 2. If you are brain in a vat, your experience is just as consistent as it would be if you were NOT a brain in a vat. 3. Therefore, your conclusions about the external world are equally justified whether or not you are a brain in vat. 4. Suppose you are a brain in a vat. 5. Then, everything you believe is FALSE. 13

14 Consider the case of the brain in the vat again. 1. If you are a brain in a vat, then your experience is just as involuntary as it would be if you were NOT a brain in a vat. 2. If you are brain in a vat, your experience is just as consistent as it would be if you were NOT a brain in a vat. 3. Therefore, your conclusions about the external world are equally justified whether or not you are a brain in vat. 4. Suppose you are a brain in a vat. 5. Then, everything you believe is FALSE. 6. But from (3), your beliefs are just as justified as they would be if they were true. Consider the case of the brain in the vat again. 1. If you are a brain in a vat, then your experience is just as involuntary as it would be if you were NOT a brain in a vat. 2. If you are brain in a vat, your experience is just as consistent as it would be if you were NOT a brain in a vat. 3. Therefore, your conclusions about the external world are equally justified whether or not you are a brain in vat. 4. Suppose you are a brain in a vat. 5. Then, everything you believe is FALSE. 6. But from (3), your beliefs are just as justified as they would be if they were true. 7. Therefore, according to Locke, we can say that you have KNOWLEDGE of the external world. 14

15 Consider the case of the brain in the vat again. 1. If you are a brain in a vat, then your experience is just as involuntary as it would be if you were NOT a brain in a vat. 2. If you are brain in a vat, your experience is just as consistent as it would be if you were NOT a brain in a vat. 3. Therefore, your conclusions about the external world are equally justified whether or not you are a brain in vat. 4. Suppose you are a brain in a vat. 5. Then, everything you believe is FALSE. 6. But from (3), your beliefs are just as justified as they would be if they were true. 7. Therefore, according to Locke, we can say that you have KNOWLEDGE of the external world. 8. But how is it possible that KNOWLEDGE = JUSTIFIED, FALSE BELIEF? Consider the case of the brain in the vat again. 1. If you are a brain in a vat, then your experience is just as involuntary as it would be if you were NOT a brain in a vat. 2. If you are brain in a vat, your experience is just as consistent as it would be if you were NOT a brain in a vat. 3. Therefore, your conclusions about the external world are equally justified whether or not you are a brain in vat. 4. Suppose you are a brain in a vat. 5. Then, everything you believe is FALSE. 6. But from (3), your beliefs are just as justified as they would be if they were true. 7. Therefore, according to Locke, we can say that you have KNOWLEDGE of the external world. 8. KNOWLEDGE = JUSTIFIED, FALSE BELIEF. 15

16 The problem, in other words, is that Locke must accept that false beliefs must count as knowledge, and this seems to be reasonably incoherent. How could you be said to have knowledge if almost everything think to be true is in fact false? A note on Rationalism and Empiricism Rationalism is the view that we come into the world with either innate ideas (beliefs) or an innate disposition to form certain kinds of beliefs as we develop. Empiricism is the view that the only source of our beliefs is the external world. We begin our life as a tabula rasa, a blank slate, and we get our ideas from the external world through our senses. Of course, once we have those ideas, we can use our innate cognitive skills to form other beliefs. 16

17 What distinguishes the rationalist and empiricist is a disagreement about where our beliefs come from. It is not a dispute about how to form a theory of knowledge (whatever Appiah says), or whether or not one should be a foundationalist. A rationalist need not be a foundationalist about knowledge. You could believe that we come with certain innate beliefs about the nature of the world, and yet think that those beliefs will ultimately turn out to be false. This would be the case if those beliefs were just very useful but not actually true. Many evolutionary theorists now believe this. 17

18 An empiricist can be a skeptic (an anti-foundationalist). You can believe that all of our ideas/beliefs seem to come to us from the external world through our senses, and yet think that this gives us no good reason to think that a foundational system is possible. 18