Alan Saunders: You put the kettle on the stove, turn on the gas, and in a little while the water in the kettle boils. So can we say that turning on the gas caused the water to boil? Or is it just that all we can say is that there were two events: gas goes on, water boils, but that there is no real connection between the two.

It seems like a simple question but it goes deep into our understanding of the world.

[Music] Colin's Kisses: The Music of James Oswald

Alan Saunders: It was one of the many deep questions asked by David Hume, the great Scottish philosopher whose 300th birthday we're celebrating with a month of special editions of The Philosopher's Zone.

[Music] Colin's Kisses: The Music of James Oswald

Alan Saunders: Hi, I'm Alan Saunders, and to tackle this aspect of Hume's thought we're joined today by a distinguished Hume scholar Helen Beebee, professor of philosophy at the University of Birmingham in the UK.

Helen Beebee: Hume's central thought that really all we get to find out about the world is just regularity, is just one thing following another, and then next time, one thing following another again, and somehow out of that we conjure up beliefs about what causes what—that's been absolutely central to the debate about causation as it's gone on for the last three centuries.

Alan Saunders: So he set the agenda?

Helen Beebee: Yes, he did. Yes.

Alan Saunders: Hume wrote two books of what we would now call epistemology and metaphysics: A Treatise of Human Nature and An Inquiry Concerning Human Understanding. So let's look at what he was actually trying to do. He wanted to provide a science of man (I suppose these days we should say a science of humanity) didn't he?

Helen Beebee: Yes, he advertises himself right at the beginning of the Treatise of Human Nature as providing a science of man, and I guess the thought there is he was very impressed with Newton and very impressed with experimental philosophy more generally, what we would now think of as science, but in those days experimental philosophy and philosophy were kind of all the same thing. So the idea that if you want to find out about the nature of reality the way to do it is to have a look, see how things work, do some experiments, people have started doing that when it comes to the world around us, but Hume's thought was 'Let's apply that to our own case, to moral subjects' as he called human beings.

So what he wants to do is to figure out how it is that the mind works using a similar kind of experimental method, rather than to kind of sitting in the armchair and trying to figure stuff out a priori we actually—well not exactly run some experiments, we look at how it is that the mind actually works going on our observations of what sorts of things we believe, and how we come to believe them.

Alan Saunders: Was he just trying to be the Newton of the social sciences, or are there actually targets against which he is writing?

Helen Beebee: Oh he very definitely has targets. I guess his main target is what he calls speculative metaphysics. So he says at the conclusion of all his kind of researches into how the mind works, 'Works of speculative metaphysics should be committed to the flames, because they contain nothing but sophistry and illusion.' And what he has in mind there is anyone who claims to be able to figure out the ultimate nature of reality, there are things that just lie beyond our cognitive reach.

He certainly has religion in his sights, so theologians and philosophers who claim to know things about the nature and existence of God, that sort of speculative metaphysics, that's all got to go. And when it comes to causation, the view that he mainly has in his sights is the thought that we can now a priori, just by reflecting on concepts, just by reflecting on the nature of ideas, we can come to know things a priori about the causal structure of the world.

Alan Saunders: Well let's look at what he has to say about causation, about cause and effect. Now he thinks that we can't come to conclusions about this 'a priori' which basically means sort of 'before the facts', 'without the facts', doesn't it?

Helen Beebee: Right, yes. For example, there's a well-known principle ex nihilo nihil fit, which basically translates as something like 'nothing can come from nothing'. Now, that's a principle that prior philosophers had wheeled out typically in arguments for the existence of God. The thought is that it's an a priori principle that every event has a cause, because otherwise that would be something coming from nothing, and now well if every event has a cause, then that couldn't go on forever, backwards in time, so there must somehow be a first cause that was somehow a cause of itself, or a necessary existence so that it didn't need a cause, what's that going to be? That's going to be God.

Alan Saunders: Looking closer at causation, let's take the time-honoured case of the billiard ball. The idea is that we see the white ball hit the red ball and the red ball moves. But we don't actually see the white ball cause the red ball to move. All we see are two separate events and we can't actually see the connection, if there is a connection between the two. So the world is, as it were, just one damn thing after another; we can't see or prove any connection between events. Is this Hume's view?

Helen Beebee: Well it's certainly Hume's view that we can't prove any connection between events. And it's also true in his view that we can't see any connection in the sense of there's no sensory impression as Hume would put it, of causation, there's nothing, as you say, when you look at the two billiard balls you just see the one hitting the other and then the other one moving, you don't see any connection. So there's no sensory impression of causation.

And Hume thinks that creates a problem because he thinks that all of our ideas, which we could think of as concepts, come from impressions. So if we're going to have the idea of causation at all, which clearly we do, somehow we have to have an impression of causation or necessary connection as he calls it. But that impression can't come from experience; you get the impression of red just by looking at a red thing; you can't get the impression of necessary connection just by looking at things happening in the world because you just won't find any such impression there.

Now what the consequences of that are on Hume's view is kind of a wildly controversial issue. So some philosophers think that the consequences that Hume thinks that causation just is a matter of constant conjunction, that's all there is out there in the world, and when I say one thing caused another, all I mean is things of the first kind are constantly conjoined with things of the second kind. So every time a white ball hits the red ball in just those sorts of circumstances, the red ball will move off in the same way. That's all there is to saying that one thing caused another.

On another view, and I guess in some moods this is my view of what Hume's doing, Hume thinks that causation is something that we kind of project on to the world. So out there in the world—or at least as far as we can know—all there is is just one thing happening and then another. But then we have this impression of necessary connection which is just the creation of a human mind which we somehow impose on reality, so we kind of invent the causal structure of the world.

On another view, Hume actually does think that there is such a thing as causation out there in the world, he really does think that there's a necessary connection between causes and effects. It's just that he thinks that we can't detect it, but he thinks that when we talk about causation, that really is the thing we're talking about, some kind of real connection out there in the world between causes and effects. He's just sceptical about our ability to detect or know about that relation. So there's a huge range of views to choose from about what it is that Hume actually thinks.

Alan Saunders: And which side do you come down on?

Helen Beebee: I kind of come down in the middle, on the sort of projection side I guess. Hume thinks that the causal structure of the world is something that we impose upon it, but I suppose I'm a bit inclined to think that actually the metaphysics of causation; the nature of causal relations, or what it is that the word 'cause' refers to, is not that much of a concern for Hume anyway really, what he's really interested in is how these beliefs come about, what their epistemic status is, and so on.

And we can agree on all of that stuff and still leave it open what he actually thinks the word 'cause' refers to. So there's a sense in which we don't really need to resolve that dispute about what Hume thinks about the metaphysics of causation in order to agree about what he thinks about the things that he really cares about, which is the kind of the psychology and the epistemology.

Alan Saunders: I'm interested in Hume's view of what's called the association of ideas. Now if you're an empiricist, if you think that most of our knowledge of the world comes through our sensory impressions, as you've said, you need to find some way of explaining how these impressions build up into a view of the world, and that's where association comes in. But for Hume, what does it amount to?

Helen Beebee: Yes, so for Hume I guess association amounts to the thought that anything that's going on in your mind kind of unconsciously or instinctively is going to be a matter of the association of ideas. So ideas are faint copies of impressions—you see red and thereby have an impression of red, and now your idea of red, the kind of the thing that you used to think with, when you're thinking about red, is kind of derived from that impression.

But the most important part of association for Hume is the relation between causes and effects, so the question—or at least I think the question for Hume—is how is it that we start out with all of these impressions and the corresponding ideas, and we go from that to a situation where we actually come to have beliefs or expectations about what's going to happen.

So for Hume, a belief is a kind of lively idea and the question is, OK, now we've got the idea, where does the liveliness come from? How is it that we absorb all of this stuff, and out pop these actual expectations that are not just responses to what's in front of us but actually views about what's going on outside of our experience; my expectation that the sun's still going to be shining when I go outside, that my car's going to stop when I put my foot on the brake and so on. How is it that we get to have those things in our mind? Hume's answer is reasoning from causes to effects which he thinks of as just an associative relation.

Every time you sit in your car and you put your foot on the brake, the car stops and once that regularity has been established in your experience, the next time you put your foot on the brake, you just come to expect that the car's going to stop. You're not doing any fancy piece of reasoning there, it's just a habit or a transition in the mind that takes you from the regularity in your past experience to an expectation about what's going to happen. So that's a kind of really brute, crude psychological mechanism, it's one that just happens instinctively.

Alan Saunders: Well yes, a brute psychological mechanism—does there have to be any logical connection between the ideas that we associate, or are we all like Pavlov's dogs? We come to associate a ringing sound with food, even though there's no logical connection between bells and dinner.

Helen Beebee: Yes, so I think Hume thinks we are a little bit like Pavlov's dogs, there are at least in our unsophisticated moments we are. One of the things that Hume is at pains to prove, and that goes back to his target being people who think that you can have a priori access to the causal structure of reality, one of his central claims is 'Look, there is no logical connection between causes and effects.' For anything you can figure out a priori, anything could cause anything.

So you think when you put your foot on the pedal the car is going to stop, but a priori anything could happen if you put your foot on the pedal. The car could speed up, or it could turn into a pumpkin, you could rise up in the air and start spinning around. There's no logical reason why putting your foot on the pedal is going to make the car stop. So if you think about Pavlov's dogs again, I mean of course Pavlov's dogs are in an experimental set-up that someone has kind of rigged up so that the bell-ringing isn't really a cause of the dog getting the food, but maybe the dog thinks it is. So we like to think that putting your foot on the pedal really is a cause of the car stopping, but as I say, that's not because we've intuited or experienced any causal connection between them and it's certainly not because there's some sort of logical connection between them. The first time you get in a car, if you've never seen a car before, you're going to have no idea what's going to happen if you stick your foot on that pedal.

Alan Saunders: So is this an important discovery on his part? I mean does it make us think differently?

Helen Beebee: Yes. Well I don't know if it makes us think differently now, but certainly at the time, I mean he got a lot of his material here from Malebranche, it must be said.

Alan Saunders: This is the French philosopher of the 17th century.

Helen Beebee: Quite, yes. So Malebranche shared the view that we couldn't perceive any causal relations with Hume except that Malebranche went off in a very different kind of religious direction, thought that God was actually the cause of everything. Seeing as we can't see a causal relation between the billiard ball hitting the other billiard ball, and the second billiard ball moving, well there can't be a causal relation there, it must be caused directly by God. All of these things are being caused directly by God. Of course Hume didn't take that line.

So he got the idea that we can't perceive causation from Malebranche. Nonetheless the thought that there really isn't anything there that we could possibly detect, I think is quite a sort of striking and revealing philosophical result, and it does urge caution on us when we think that we know things about the causal structure of the world, to be kind of reminded if Hume's right about this, and I think he is, that really what's in front of us, what we see as one thing and then another thing happening.

Alan Saunders: On ABC Radio National, you're with The Philosopher's Zone, and I'm talking to Helen Beebee from the University of Birmingham about David Hume's views on causation and induction.

Helen, we've dealt with causation, let's now turn to the related question of induction, and first of all, what is induction?

Helen Beebee: Well induction means different things to different people. In the context of contemporary philosophy, inducted inference is normally seen as going from regularities that you've experienced in the past to some universal generalisations. So As have always been followed by Bs in the past, therefore all As have been followed by Bs. For Hume, inducted inference he's less concerned I think about—the kind of the very general cases more concerned about All right, all As have been followed by Bs in my past experience; now I'm confronted with an A, what's the mechanism by which I come to expect that a B is going to happen?

So he's more interested kind of in the single case I think, rather than the kind of general laws. So in contemporary philosophy the problem of induction is thought of as a kind of problem in philosophy of science. How is it that we can know what the laws of nature are? Whereas I think Hume was more worried about how can you be sure that your car's going to slow down or not (well not our car, obviously).

So the problem of induction is now the problem of justifying that inference. How do we go from all As have been followed by Bs in the past to All As are Bs or the next A is going to be a B? What licenses that inference? And that's the problem that Hume's commonly thought to have both raised and also shown to be completely insolvable.

Alan Saunders: And it doesn't have to be time-related, it can be a generalisation about the present as well. All the crows that I know are black, so from that I draw a universal law that all crows are black.

Helen Beebee: Right. Yes. So Hume's concerned because he thought of inductive inferences as basically inferences from causes to effects. He was thinking of inductive inferences being As followed by Bs, right, because that's the cause-effect relation. Whereas since Hume, people have kind of generalised out and thought of it not necessarily as being a matter of all As are followed Bs, but as you say, all As are Bs, or all crows are black, all swans are white is the famous example, and so on. So from the point of view of the problem of induction it doesn't matter which way you do that, but Hume is only worried about As being followed by Bs, because he's worried about inferences from causes to effects.

Alan Saunders: And all swans are white is a notoriously good case of the inadequacy of induction because you go to Western Australia and there you've got black swans.

Helen Beebee: Absolutely.

Alan Saunders: We might try, rather shonkily I think, to justify induction by saying that it's worked in the past, so there's good reason for thinking that it will work in the future. What's wrong with that?

Helen Beebee: Yes, that is one where you might try and do it, and it's quite similar to a way that Hume considers and dispenses with, and this way is going to fail for just the same kind of reason, which is that of course the very claim that it's worked in the past so it's going to work in the future is itself a form of inductive inference. So if you want to try and show why inductive inference is all right, you'd better not appeal to something which is itself an inductive inference in order to do that. That's just not going to satisfy someone who's already suspicious about whether inductive inference is okay.

Alan Saunders: Karl Popper, writing in 1934—this is the great 20th century philosopher of science—referred to the problem of induction as 'Hume's problem'. For him, it was essentially insoluble. He thought that it is simply incorrect to assume that just because the sun has risen every day so far, it will rise tomorrow. From that emerges his philosophy, which is basically that we should seek to disprove rather than to prove our theories. But was Popper's problem really Hume's problem? Is the problem that he sees before him the problem that Hume saw before him?

Helen Beebee: I think Popper sets off a genuine disagreement between him and Hume, which is to do with whether we actually use inductive inference. So Popper not only thought that we should follow the method of conjecture and refutation—you throw up a hypothesis and then you test it—but he actually claimed that that's how we really do go about our ordinary lives, that is how we reason. And that's how dogs reason as well.

Now that stands in complete opposition to Hume, who thought that inductive inference; inference from causes to effects, was the thing that is the inference that we rely on all the time. So Popper thinks that's just false, it's not that we expect the car to stop on the basis of the fact that it stops when we put our foot on the pedal every time in the past, it's more that we have a hypothesis that in general the car stops when you put your foot on the brakes, and now we test that hypothesis in a rather high-risk fashion by going around and driving down the motorway and hoping that this time our hypothesis is not refuted.

In general, Popper thinks in science it's good when a hypothesis gets refuted because that shows you that it must be false. In the case of driving your car, you might worry about whether it's such a good idea if your hypothesis is refuted or if that's something you should be hoping for. So he genuinely disagrees with Hume over whether or not inducted inference is the form of inference that we use to go about our daily lives, or indeed in scientific investigation.

Whether the problem of induction is characterised as a problem about justification is Hume's problem, is something that I'm not so sure about. In fact I think it's not Hume's problem at all. I think Hume's problem is to do with the psychology of our beliefs or expectations. How is it as a matter of fact that we get from observing regularities in the past to coming to form this expectation about what's going to happen? What's the mechanism that does that?

Alan Saunders: So what you seem to be saying is that for Hume, the problem of induction is actually a psychological issue?

Helen Beebee: Yes, that's what I think. At least when he's discussing what's now called the problem of induction, I don't think he's discussing an issue about justification; he's discussing an issue about the psychological mechanism where you go from a situation where you have no beliefs or no expectations to a situation where you do have expectations. And he's aware that there's a major sceptical problem here, but I don't think that makes him a sceptic.

I mean his response to the sceptics, such as it is, is basically to say, 'Well, you know, if we all followed your advice and suspended belief, rather than having these expectations and trusting them, we just kind of said 'Well I have no idea what's going to happen' we'd all die, very quickly. And that's his response, you try and live like that, you won't even—you won't last a day.

Alan Saunders: So basically we have an input-output model of the mind. Sense impressions are the input, belief is the output, and Hume was interested in how we get from the one to the other.

Helen Beebee: Yes, that's the idea, yes. So in the case of our billiard balls, our As and Bs again, once I've acquired sufficient experience of As being followed by Bs, that's the thing that generates the mechanism, so now next time I see an A, what happens is that I'll end up with an expectation that a B will happen, and what is that mechanism? Well obviously that would be a kind of a question for a neuroscientist, Hume doesn't know how to answer it, he said it's habit or custom. We just get used to these things going together, this is associationism again, these things have gone together in our past experience—we come across a new A, we just by sort of a brute psychological mechanism, which we share with dogs, come to expect a B on the basis of that.

I mean again, that's not going to satisfy the inductive sceptic, right? Because the sceptic is going to say, 'Well, we have no more reason to think that the dinner's going to nourish us than it is that it's going to poison us. I mean all the evidence we've got to go on is that it's nourished us in the past, and that doesn't justify any claim about the future, and Hume's going to say, 'OK, that's a valid point, but now I'm going to eat my dinner, and I'm going to be the one that isn't going to die of starvation.'

Alan Saunders: Hume gave up philosophy more or less and became a historian. The way you presented this aspect of his philosophy, it sounds as though it's not actually leading him anywhere except back into the world, back into carrying on with your life. I mean do you think that's why he gave it up?

Helen Beebee: I wouldn't want to speculate about why he gave it up. But I guess, I mean if you think of Hume as really thinking of what he's doing is giving the science of man, then in so far as he thought that he'd got that pretty much right, I guess, and if people were not responding to...and kind of in his own terms, if you see what I mean, if they were kind of insisting on sort of pushing him on kind of abstruse metaphysical speculation which is what he thought we shouldn't be doing, then I can kind of imagine that he might have thought, 'Well OK, I'm going to wait until someone actually comes along with some hard experimental data that shows me that my kind of psychological views are all false, and then maybe I'll get interested again,' and I don't know, maybe nobody did.

Alan Saunders: Well these are tangled issues but Helen Beebee thank you for untangling Hume's view of them for us.

Helen Beebee: Thank you very much.

Alan Saunders: Helen Beebee is professor of philosophy at the University of Birmingham in the UK. More about Hume on our website.

The Philosopher's Zone is produced by Kyla Slaven, the sound engineer is Charlie McKune, and the music today was from the Scottish composer James Oswald, who died in 1769.

[Music] Colin's Kisses: The Music of James Oswald

Alan Saunders: And I'll be back next week to find out what Hume had to say about why we should behave well and what it is to behave well.

[Music] Colin's Kisses: The Music of James Oswald