 Hi, I'm Peter Adamson and you're listening to the History of Philosophy podcast, brought to you with the support of King's College London and the Leverhulme Trust, online at www.historyofphilosophy.net. Today's episode, I know because the caged bird sings, Plato's Theaetetus. Those of you who spend time with children will know that between the adults and the children of this world, a war is raging. Skirmishes in this war are fought across the land, every morning, and both sides use all the weapons at their disposal, tantrums, the silent treatment, withheld treats, even in extreme cases, the naughty step. I am speaking of course about the question of how warmly to dress. The children's perspective on this issue is well entrenched. It is not nearly as cold outside as you parents would claim, and we aren't going to wear that winter coat, though we may be willing to consider a light sweater. The parent's point of view is equally firm. You'll catch your death of cold. Now, I guess that most of the people listening to this podcast are above the age of 12, and so naturally favour the adult perspective. There is, we quite naturally think, a fact of the matter about how cold it is outside. Just look at the thermometer. Yet the children can turn to us and say, but I don't feel cold, so for me it isn't cold. And they've got a point, albeit a point which is undermined slightly when they start shivering, even as they're insisting on how warm it is. The point is that it is for each person to say how cold the air feels to them. You might even say that, whatever the temperature may be, the air's being cold is nothing more than the air's seeming cold to each of us. This prompts an unsettling thought. It's not implausible that the air is really neither cold nor hot in itself, but is cold for you and warm for me. I grew up in Boston, so I'm made of tougher stuff than you are. And we can think of other cases. Most of us have been in disputes about whether a certain piece of clothing is blue or green, and maybe it is just green for one person, blue for someone else. Thus, the unsettling thought, what is everything like this? Suppose that there is no truth apart from the way things seem to each person. Things may be warm for me, cold for you, blue for me, green for you, good for me, bad for you, while having none of these features in themselves. In that case, nothing is true absolutely. Rather, truth is relative. Something might be true for me and false for you, but neither false nor true in itself. This relativist theory of truth is one that still arises in contemporary philosophy, but it has its roots in the dialogues of Plato. In particular, it is explored in my very favourite platonic dialogue, the Theaetetus. In a few previous episodes, I've mentioned the word epistemology, which means the study of knowledge, because the ancient Greek word for knowledge or understanding was episteme. We saw last week that Plato's Meno has quite a bit to say about epistemology, and we found interesting epistemological ideas already in the pre-Socratics, but the first work to devote itself fully to epistemology is the Theaetetus. It explores some of the ideas of the Meno but goes well beyond them, investigating not only this relativist theory of truth, but also the question of how false judgement is possible and how knowledge relates to belief. The main characters are our old friend Socrates, Theodorus, a mathematician, and a young man who is a mathematician like Theodorus and profoundly ugly like Socrates. He shares Socrates' protruding eyes and snubbed nose. This is Theaetetus, one of the most admirable characters ever to engage with Socrates in Plato's dialogues. Despite his youth, he shows much more commitment to the philosophical search than the older Theodorus. He offers several attempts at saying what knowledge might be. As we have come to expect in Socratic dialogues, each attempt is refuted, but he doesn't lose heart, and we learn a great deal about knowledge in the course of the dialogue even if the characters fail to produce a definition of knowledge that satisfies them. Theaetetus' first attempt is to say that knowledge is perception. The word for perception here is isthesis, which incidentally is where we get the word aesthetics. It can mean sense perception, that is vision, hearing, smell, and so on, or more broadly any kind of perception, including the perception of things with the mind. Especially if we take it in this broader sense Theaetetus' definition looks plausible, we know something when we perceive it. Or perhaps one might say, we know when we grasp that something is the case. But Socrates shows that Theaetetus' definition could be taken in a more unsettling way. If knowledge is perception, then whatever seems to me to be the case must actually be the case for me. Here he gives the same example I used a moment ago. The wind seems warm to me and cold to you, so I perceive the wind as warm and you perceive it as cold. If perception is knowledge, then that means that I know the wind is warm and you know it is cold. How could this be? Well, only if truth is relative. It's true for me that the wind is warm, and true for you that it is cold, but there is no such thing as the wind's being truly warm or cold in itself relative to no perceiver. After all, knowledge is nothing but perception. Socrates adds that, in putting forward such a view, Theaetetus would be more in good company. In particular, this relativistic theory of truth was asserted by the great sophist Protagoras. As we saw in our previous episode on the sophists, Protagoras was famous for saying, man is the measure of all things, of the things that are that they are, of the things that are not that they are not. Like Theaetetus' definition of knowledge as perception, this man is the measure doctrine could be taken in a lot of different ways. But Socrates wants us to take both claims as boiling down to relativism about truth. If I am the measure of whether the wind is warm, then there is nothing more to the wind's being warm than it's being warm for me and not cold for me. The way things seem to me determines the way the wind is and isn't for me. But wait, there's more. Socrates adds that Theaetetus and Protagoras have another heavy hitter on their side, namely the pre-Socratic philosopher Heraclitus. You might remember that when I talked about Heraclitus, I said that Plato portrays his illustrious predecessor as believing in a doctrine of total flux. That is, everything is constantly changing in every respect and there is no stability in us or the world around us. The Theaetetus isn't the only dialogue where Plato ascribes this view to Heraclitus, though it is the most famous example. But why does the flux doctrine go along with relativism about truth? This is a slightly complicated question, but the basic answer is that if protagorean relativism is true, then the things in the world around us will have no stable natures from moment to moment. They will only be whatever they seem to be to various perceivers and this is changing all the time, according to Heraclitus as he's presented here. So, on this view, it would turn out that nothing is cold and nothing is warm. Rather, everything is always changing in every way. Actually, it might be even worse than this. If we say that what is changing from warm to cold or vice versa is both warm and cold, then the air will always be both warm and cold. It was with this in mind that Aristotle later accused Heraclitus of denying the principle of non-contradiction. These radical consequences of the flux doctrine give us plenty of reason for rejecting it, and if buying into the relativist theory of truth means buying into the flux theory, then maybe we'll give up on relativism as well. But protagoras will try to persuade us that the relativist theory isn't as implausible as it seems. If you're interested in which things are good, then obviously what you're interested in is which things are good for you. What would it even mean for something to be good but not for you or for anyone in particular? This perhaps connects the theory Plato is considering to the real historical protagoras. He claimed to teach virtue, and may have supposed this was possible because the good is the advantageous, and that he could teach you how to get things you would consider to be advantageous, like political power. Whether protagoras really held the radical epistemological theory that Plato ascribes to him here in the Theaetetus is of course another matter, but let's leave that aside, and also leave aside the problems about flux and just consider the problem of how to refute someone who adopts the relativist position on truth. Now I know what you're thinking. This will be easy. Just point to a thermometer, which tells us an objective fact about how cold the air is, but not so fast. Firstly, protagoras can agree with your kids that whatever the thermometer says, it's up to each of us to say whether it is cold or warm for us. Secondly, he can point out that the thermometer is itself something you perceive. If it seems to you that the thermometer reads say 30 degrees, then it's true for you that the thermometer reads 30 degrees. It's true for you simply because you perceive it to be the case. To insist on there being an absolute truth about the reading of the thermometer is just to assume that there is a truth independent of any perceiver, and that's what protagoras denies. Man is the measure of all things, right? But Socrates has a couple of other tricks up his sleeve. He starts with abuse. Wouldn't it be just as true to say that a pig or a baboon is the measure of all things? Abuse is always satisfying of course, but this argument doesn't carry much weight. Fortunately, he has more philosophically satisfying points to make too. For instance, on this man is the measure doctrine, there'd be no point consulting experts. Why pay to go to the doctor if you are just as good a measure as the doctor is? If it seems to you that taking aspirin will cure that nasty bout of appendicitis, then it's true for you. This sounds like a theory that will reduce the life expectancy of its adherents, reason enough to reject it. Closely related is an objection about predicting the future. If I expect to recover from my illness, then it will be true for me that I will recover. If it then later seems to me that I'm still sick, then it will seem to me that I have not recovered, and so it will be true for me that I didn't recover. It's hard to see how both of these could be the case. But Socrates' most interesting objection illustrates a classic, perennially useful philosophical maneuver. Whenever you're presented with a bold new theory, especially a skeptical theory, ask whether the theory could be true on its own terms. For example, if someone says that nothing is true, you can ask him whether this claim is itself true. Or if someone says that language is meaningless, you can ask him how he is able to convey this idea in a sentence. In the same way, Socrates suggests that Protagoras' relativism doctrine is self-refuting. For, even if Protagoras agrees with the doctrine, Socrates does not. Thus it will be true for Socrates that Protagoras' doctrine is false. Indeed, since this follows from Protagoras' doctrine, it will even be true for Protagoras that for Socrates the doctrine is false. Thus, Protagoras is bound by his own doctrine to admit that his doctrine is false. But maybe this trick is a bit too tricky. Even if Protagoras has to admit that the doctrine is false for Socrates, he doesn't have to admit that it's false in itself, or really false. Remember, according to him, there's no such thing as something's just really being false or true. There's only something's being false or true to you, to me, to Socrates. Before we get any dizzier, let's leave relativism behind and move on to another major theme of this dialogue, the possibility of false belief. This theme arises when Theaetetus accepts that knowledge is not, after all, perception, and makes another suggestion. Perhaps knowledge is having a true belief. After all, when I know something, I have a belief about it, and obviously it can't be a false belief, so why not say I know something when I have a true belief about it? All well and good, says Socrates. But if we want to uphold this definition, we need to understand how it could be that some beliefs are true, and others false. And here we will run afoul of those pesky sophists again. Some sophists suggested that it is impossible to say or believe anything false, in which case everything is just a matter of persuasion. This challenge appears in several Platonic dialogues. We've already seen it arising in the Euthydemus, but the Theaetetus is again probably the most famous case. The argument here for the sophistical view is rather reminiscent of Minos' paradox, which we looked at last time. It goes like this. Either I know something or I don't. If I know about it then I won't make a mistake about it, thanks to my knowledge. But if I don't know about it then I can't think about it, so I won't be able to make a mistake then either. In other words, I'll have either perfect knowledge of each thing, or no knowledge of it at all, and in neither case will I get things wrong. So it's impossible to make a mistake, to believe anything false. As with Minos' paradox, it looks like the way out is to say that there is some middle ground where I know or grasp something well enough to make a mistake about it, but not so well that I am immune to error. Socrates presents two analogies to suggest how this could work. First he says, imagine that your memory is like a wax tablet, the kind they used to write on in ancient Greece. When you perceive something, that's like a stamp making an impression in the wax of your mind. Some people have tough, dirty wax and are slow on the uptake, others have fluid wax and get impressions quickly, but lose them just as fast. Others have wax which is ideally suited, easily stamped, but also good at holding the impressions. Quite a nice image of how memory works, really. Okay, so now for false judgement. That would happen when there is a mismatch between something you perceive and an existing impression in the wax of your memory. For instance, I think I am watching a silent film starring Buster Keaton, but actually I'm confused. That lovable fellow on the screen is in fact Charlie Chaplin, and I'm matching the visual image to the wrong stamped impression in my wax tablet. As Socrates says, it's like putting your right foot into your left shoe. Notice that this solves the sophisticated dilemma. I can make a mistake about something because in a way I know it, and in a way I don't. I know who Buster Keaton is because I must have got acquainted with him to have an impression of him in my memory, but this doesn't guarantee that I'll be error-free in identifying people as Buster Keaton. This is a compelling analogy and for once the proposal isn't exactly rejected in the dialogue. Rather, the characters realize that even if it works for cases of mistaken identity and perception, there are many cases of false judgement where it will not help. For instance, what is going on when I add 7 and 5 and get 11? There's nothing here about impressions being made on our memory by perception, and yet I've still made a mistake. So Socrates produces another image in place of the wax tablet. Imagine, he says, that your soul is like an aviary, a bird cage, with lots of birds flying around in it, each of which represents a piece of knowledge. Whenever you've learned something, you've acquired a bird and put it into your aviary. What happens when you add 5 to 7 and get 11 is that you reach into your aviary and pull out the 11 bird instead of the 12 bird. Again, your knowledge of 11 actually enables you to make the mistake, the way your knowledge of Buster Keaton enabled you to mistake Charlie Chaplin for him. But Socrates and Theaetetus decide that this model too is problematic. It means that when you make a mistake, it is precisely by virtue of knowing that you get things wrong. It is paradoxically because of your knowledge of 11 that you are able to have a false belief about 5 plus 7. The indefatigable Theaetetus has another suggestion though. What if your aviary contains birds representing ignorance as well as birds representing knowledge? Then when you make a mistake, you've just grabbed the wrong kind of bird. But that ruins the whole point, which was to explain how we can know something just enough to make a mistake about it without knowing it so well that we are immune to error. So, where does all that leave us? Right back where we started, without a general account of false belief, but still thinking that maybe knowledge is the same thing as true belief. Ah, but it isn't, says Socrates. Just consider the case of a jury. They might be persuaded by some fancy lawyer that a certain man is innocent of a crime. And the man really is innocent. But we wouldn't say that the jury knows, since they only believe this because the lawyer was slick enough to persuade them. Thus, they have a true belief, but not knowledge. So much for that definition. Yet, Theaetetus still feels, and today's epistemologists tend to agree, that knowledge must have something to do with true belief. Maybe knowledge is true belief plus something else as well. Something the jurors are lacking, but which you would have if you were, say, an eyewitness at the murder, and know that the accused man is innocent. It's no easy task to say what that would be. As I say, modern day epistemologists are still struggling with the question of how knowledge relates to true belief. In so doing, they are taking up a challenge first thrown down here in Theaetetus. For the rest of the dialogue, Socrates and Theaetetus explore the possibility that some kind of rational account, a logos, that favorite word of Heraclitus, is what you'd need to add to true belief to render it into knowledge. As we expect by now, they don't manage to make this work, and yet we do learn a bit more about knowledge, in particular, how it does and does not relate to giving an account of yourself when you believe something. This last part of the dialogue is sufficiently complicated that giving an account of it would be no easy matter, and I'm just about out of time anyway, so I'll close there for now. But Plato's attitude towards belief and knowledge will continue to take center stage in the next few episodes. In two weeks, I'll finally be looking at Plato's theory of forms, and trying to discover whether postulating forms could help us understand what knowledge is. But next time, we'll have a return appearance by my colleague M.M. McCabe, who will chat with me about Plato's views on knowledge. So, don't make the mistake of missing next week's episode on the history of philosophy without any gaps.