2021-06-15 ToKCast David Deutsch answers a question about truth. A question for David 4
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Duration: 00:15:21
Transcript
Brett Hall
Philosophers have invented many different theories of truth over the years. The three most prominent ones that I’m aware of are something called the coherence theory of truth. That’s where a statement is true if it doesn’t conflict with other things that we know are true. So it’s coherent with everything else that we know. That’s the coherence theory of truth. The pragmatic theory of truth is that a thing is true if it works. So if something works as an explanation or as a fact about something, then we say it’s true. The third one is called the correspondence theory of truth. This is where a thing is true insofar as it corresponds to some aspect of reality. Popper was persuaded of this correspondence theory of truth and he writes about it in Objective Knowledge in an essay called Two Faces of Common Sense. I’m going to read just a part of it here because he expands upon this notion of the correspondence theory of truth by introducing a new term, a neologism. Popper wrote, And so he goes on. He’s referring there to Alfred Tarski, his friend and another philosopher who convinced him of this idea of the correspondence theory of truth. Now this idea of nearness to truth or closeness to truth is kind of reminiscent of chapter two of The Beginning of Infinity, which is titled closer to reality, not closer to truth, but closer to reality. So it was interesting to me that there’s this kind of similarity. Why did David choose closer to reality and not closer to truth? Is it a big deal? Is there anything lurking there that would be interesting? Well, I’m about to ask him a question about this. And if you want more, you can go to the Oxford Karl Popper Society, where on YouTube, David has given a talk precisely about this whole concept of truth. It’s a very interesting analysis, different to what I’ve heard anywhere else, anyone talking about truth. He doesn’t deny the existence of truth. He’s not a relativist, but he explains why we can’t utter truth. Truth, as he will explain, applies to propositions. For example, the content of mathematics or the content of logic. There we use variables in order to represent propositions, but we can’t utter, we cannot speak propositions. We can speak statements, which as David says are at best approximations to propositions. Mathematics, logic, they deal in these abstract propositions. And we use letters like P and Q. And we say if P is true and Q is true, then the conjunction of the two, P and Q, must be true. But even those letters, P and Q, aren’t exactly propositions themselves. They represent propositions in much the same way as the numeral for two represents the number two. But we can’t write down the number two. We can only write down things that represent that number. So mathematics and logic, for example, are not about proving things true.
Brett Hall
They’re about proving things. It’s quite different. We assume that if, for example, if the axioms that we begin with are true, then what happens at the end of our proof would produce something that’s true. But we can’t prove that the axioms to begin with are true in the first place. And indeed, every other area of our knowledge is kind of like this. Science and history, morality and philosophy. They’re all claims about this underlying reality. But we can’t say ultimately true statements about any part of that reality. The best that we can do is to make guesses. We can conjecture facts and explanations about that reality. And by refuting some of those guesses, some of those claims, we end up over time describing and explaining that reality with ever greater fidelity. As we refute the things that we have discovered can’t be true. And in this way, either a thing we say about reality is correct or it’s refuted. There’s no probably about it. There’s no gray area, gray zone here. A thing is either the best explanation that we’ve got right now or it’s been refuted. And in either case, that simply is the case. It’s not 50% refuted or 50% accepted. And in the answer today that David’s about to give me, he’s going to say something about probability as well. And he says that probability is basically a scam. And for more on that, see this wonderful talk that he gave. I think it’s very under appreciated. Out of all the talks and David’s given so many talks over the years, this is absolutely one of my favorites. It’s just his voice and some slides, but that’s more than enough. It really is a tour de force of philosophy, really getting at the heart of certain epistemological facts and explanations about why the importation of probability into a vast array of fields is simply misconceived. Not least because in so many fields, economics, say, or the financial system, not to mention science, of course, guessing the future means guessing the content of knowledge yet to be created, an impossibility. David goes through a whole bunch of fields. He puts them up there on the screen and then proceeds to cross them out one at a time after he’s given an explanation about why probability doesn’t apply in that area. So you cannot assign probabilities to almost anything except some very, very narrow things. People have asked me over the years, where can we assign probabilities? Well, only in those places where we know human knowledge cannot possibly have an effect on the outcome. A game of chance is a reasonably good demonstration of this. You can know everything there is to know about roulette. That won’t help you beat the casino. Indeed, it tells you that in the long run, you will lose or you will probably lose, which is circular, of course. But whatever the case, your creativity won’t affect the likelihood of the ball coming up number 14 or on red and so on.
Brett Hall
The odds are, in other words, fixed and they’re fixed in favor of the casino. But in the rest of human life, almost, the odds are not fixed. We take action to change the odds. What’s the chance of having a car accident? Well, you could probably look up statistics, sure, but you personally might be a much worse driver. You personally might have terrible misconceptions about driving that other people don’t have. The chance of a car accident in your area on a Tuesday afternoon might be one in 10,000, but that might not apply to you. You may drive in a more hazardous way. It might also be the case that the authorities have recently used their creativity to change parts of the road. For example, speed limits, which just change the probability in a way that you couldn’t predict and that the statistics could not have taken into account prior to the change in the speed limit. So much the worse for long-term scientific predictions. Our favorite example is the probability that the sun will expand into a red giant within the next 10 billion years. Ask a typical astronomer and they’ll tell you that it’s almost certain, given what we know about stars like the sun. Of course, this assumes that no one in the next 1 billion years will be able to do anything about what happens to the sun in 10 billion years. That example really is a parable more than anything else for our more pressing concerns, like the prediction that there is a 50% chance that the Greenland ice sheet will completely melt within the next thousand years. Based on people not doing anything about it, probability tends to lead to spurious predictions, which we call prophecies. Guesses about the future that assume human creativity can have no impact on the outcome. I’ve always liked this prediction prophecy distinction because it sharpens up a couple of words that otherwise mean similar things. Neither is a neologism, an invented word. I asked David about all of this, as well as this concept that Popper had of verisimilitude, because after all, it is a neologism. You mentioned that piece of prosaic terminology explanation that we all use, but I think that you’ve put a spin on it that is quite helpful. Turning to another word, a word that you in fact don’t use, and it brings me to chapter two. Don’t worry, I’m not going to go through every single chapter chronologically, but there are just a few of them. Chapter two is titled closer to reality. But Karl Popper had this term verisimilitude, which means something like closer to truth. It seems to me you’ve deliberately avoided that word, but why? Is it because it contains a misconception, it’s misleading, or it’s a needless neologism? What would be the reason to avoid such a word?
David Deutsch
I think all of those things, and I think even Popper, I don’t know the history of this very well, but I think even Popper went off it. Popper in general was very into logic. This is, I think, partly a sign of the times that the people who were doing the prevailing philosophy of science at the time, and positivism and logical positivism, many of them were logicians and mathematical logicians even. Popper originally didn’t want to mention truth at all, and then he got converted by Tarski, and he tells a story about how they were sitting on a park bench in Vienna, and Tarski explained the correspondence theory of truth to him, and he realized that this is in fact a useful concept after all. But I wonder what The Logic of Scientific Discovery would have looked like if he had in fact written the whole of it without ever mentioning truth. I think it would have been worse in some ways in that it’s difficult to make the case for realism if you don’t have a concept of truth, and Popper was very keen to formulate a realistic philosophy of science. But on the other hand, when you do introduce truth, and especially verisimilitude, then the idea is that somehow we can utter truth, or at least we can utter something that’s 90% true or something like that. And we’d have thereby a method of measuring that 90%. I think verisimilitude was not intended to be something you could measure. But if you can’t measure it, then its only use is a sort of philosophical regulating principle. And I think knowledge and problems are much better concepts. Probably Popper’s fundamental concept, the way it turned out after all these experiments with different conceptual frameworks or whatever, is the idea of a problem. Because that comes up not only in his philosophy of science, but in his political philosophy as well. And more generally, he generalizes it to even the problem situation of a gene. I’m not sure even I would go that far. But it’s a very unifying concept. And on the other hand, I don’t think verisimilitude is useful at all. And as I said, even truth, one has to be very careful to use the concept of truth only as a property of abstractions, never as something you can actually measure or have a direct access to.
Brett Hall
So therefore, would you avoid even saying that scientific explanations, or indeed explanations in any domain that we happen to be interested in, would even be approximately true? Because that would also entail some kind of quantitative claim about how close we are. Or can we still use that word? Can we still say, it’s approximately true? Or there’s some degree of accuracy in this claim about reality?
David Deutsch
I think we can use it. Because again, depending on the problem situation, if one is speaking informally, then one can use imprecise terminology. I just caught myself just a moment ago saying probably. I’m generally opposed to the whole concept of probability. I think it’s a scam. But that doesn’t mean that in everyday life, we don’t know what we mean when we’re saying Popper probably meant so and so. I don’t mean that there was a stochastic process where he could have meant something else with the probability 0.15.
Brett Hall
Yeah, I often find myself catching myself precisely the same way that you said. Generally, it kind of has left my vocabulary just in day to day life using the word probably. But at the same time, I don’t, you know, chastise myself too much, because in order to communicate normally, you know, people are going to use this word. They understand, I think, what we mean.
David Deutsch
There is no such thing as a perfectly precise language. Yes. So we want to use terms and ways of understanding things that are suitable to the problem.
Brett Hall
So there we go. In any area of life, there will be reasons to use sharp language at times, which is to say, highly precise terminology. Medical doctors and pilots might want to be extremely precise in exactly what they mean when they are communicating with people in their area of work. Sometimes in broader areas of science, we want precise words and even in philosophy. But at other times, because of what David has said there, there can be no perfectly precise language, no perfectly unambiguous language. We’re going to need to use words that will contain perhaps some scope for misconception. Indeed, this is always the case. As Popper said, one of our favourite quips of his, it is impossible to speak in such a way as to not be misunderstood. In other words, you could always be misunderstood. Someone else can make a mistake about what you intended. And that’s always the case, because we are, after all, all of us, fallible.
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