Helen Beebee on Laws of Nature
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This is Philosophy Bites with me, David Edmonds. And me, Nigel Warburton. Philosophy Bites is available at www.philosophybites.com. Philosophy Bites is made in association with the Institute of Philosophy. The 18th century Scottish philosopher David Hume bequeathed to the world of philosophy a complex conundrum that remains unresolved. When we let go of a pen, it falls to the ground.

We assume that the law of gravity necessitates somehow that the pen will fall. But in fact, said Hume, we don't actually see or experience this necessary link. All we see is that time after time dropped objects fall to the ground, leading us to believe that there is some necessary connection between our letting go of the pen and its falling. The apparent necessity, Hume claimed, is all in the mind. We have no evidence for it being in the world.

Yet the laws of nature, e.g. the law of gravity, seem to have a special status. There's surely not a mere generalisation about how the world happens to behave. If all humans have two nostrils, we don't think that the then true claim that all humans have two nostrils is on a par with the claim that all objects left unimpeded will fall to the ground. The latter is not just a contingent truth. It feels like a necessary truth.

Helen Beebe of Birmingham University, who shares Hume's scepticism about necessity, talks to Philosophy Bites about what sense can be made of the ideas of laws of nature. Helen Beebe, welcome to Philosophy Bites. Thank you for having me.

The topic we're going to focus on today is laws of nature. What is the law of nature? Well, that's the big question really. If you think about what scientists get up to, a lot of the time certain kinds of generalisation are dignified with the title law. So you have Newton's laws of motion, you have Coulomb's law, you have the ideal gas law and so on and so on.

And these are not just any old generalisation, they seem to have some special status. So the question is what's the difference between a law of nature, say one of the laws of motion on the one hand, and a mere generalisation that happens to just describe the way things happen to be on the other hand. So could you just clarify what you mean by that? What's something that just happens to be a general law as opposed to a candidate for being a law of nature?

There are all sorts of generalisations that simply happen to be true but don't seem to have the status of law. For example, I think it's probably a truth about this room now that all the pens in it are more than three feet above the ground. Imagine that throughout the whole history of the human race, including the future as well as the past,

The oldest that anyone ever lives is to the day before their 125th birthday. So now it's a true generalisation that no human beings live beyond the age of 124. But that seems to be a kind of purely contingent accidental fact about the universe. I mean, there might be some upper bound on how long humans can live for, but it's probably not exactly until your 125th birthday.

Looks like the person that died before that day could have lived an extra day or maybe some other people who hadn't got run over by a bus or whatever could have lived beyond 125. So that's a true generalisation, not just about the past but throughout all of time, that doesn't seem to have the status of a law. OK, I understand that. There are these generalisations which just happen to be true. But couldn't that just be the same kind of thing as the law of nature? The laws of nature are just generalisations about the way the world happens to be.

Right, that is one of the standard views out there in the philosophy of laws of nature. In fact, it's a version of the view that I hold. A lot of philosophers aren't happy with that kind of view, though, because they think that laws must somehow constrain how things behave. So it doesn't merely happen to be the case that whenever you have an object with a certain mass, with a certain force acting on it, it accelerates at a certain rate. That's something that the object has to do. It doesn't merely happen to be doing that. It really has to do it.

So it looks as though, at least as what some philosophers think, the laws have a certain kind of modal status. They have a necessary status. They don't just describe how things actually behave. They describe how things must behave. So one of the issues in the philosophy of laws of nature is to try and see whether there really is such a distinction between how things must behave and how they happen to behave. And if so, whether that's a distinction that needs some kind of metaphysical story attached to it.

Metaphysics is basically the theory of reality, isn't it? The nature of reality, the way the world is, the way the universe is. And one way of looking at this could be simply that it's a convenient way for human beings to talk about their experience, to generalise in ways that allow them to predict the behaviour of objects. That tendency to generalise leads us to make into something concrete and external the law of

Actually, I agree with that completely. You can think of the laws as being sort of a list of axioms. So if we wanted to know everything that has happened and is going to happen in the universe, you could imagine kind of trying to write down every single little thing that happens, every fluttering of the leaf and every emission of a photon and so on and so on. That would be a crazily long list. Of course, it would be impossible for humans to do. But

There's another way of trying to work out what's going on in the universe, which is to notice these regularities and hypothesise that certain generalisations hold, and then you don't need to write down the emission of every photon, the fluttering of every leaf, because if you know something about the initial conditions or what happened five minutes ago or whatever, and you know the state of the leaf and the wind and so on, you'll be able to infer that the leaf is fluttering. So you could think of laws as

Just what you described, a kind of shortcut, a way of figuring out stuff about the future, starting from the assumption that the universe does in fact behave in very nice regular ways, which we all hope it does. But that hope about regularity, that's famously undermined or threatened at least by what's known as the problem of induction.

Yes, it is. Some philosophers who talk about laws of nature actually think that that's a reason not to adopt that Humean view that says that the laws of nature are really just particularly important kinds of regularity. They say that if you have that kind of view about laws...

You can't solve the problem of induction, which is basically the problem of how can we justify the inference from here's how things have behaved in the past to here's how things have behaved in the future. Now, of course, that's an inference that we draw every time. Every time we get in the car, we expect the brakes to work, we expect the steering wheel to be sensitive to what we're doing with it and so on. Why do we think that? Well, that's because that's always happened in the past.

And now the question is, what reason have we got to think that that's going to carry on happening? What reason have we got to think that next time I drop the pen it won't simply float in the air rather than fall to the ground? And again, if you think that there's some extra metaphysics going on with laws of nature, something that's constraining how things behave, then you might think that that gives us a reason to draw that inference. One standard view in the debate about laws of nature is...

that has been developed by David Armstrong in the early 1980s. And his view is that, look, if you take an object and all of its features, sort of repeatable properties that the object has, like its mass, the forces acting on it, perhaps its size, or maybe chemical properties or whatever, and he calls those universals, these repeatable features of objects, he

He thinks that what the laws of nature are are necessary connections between universals. So if you think about the law that force is mass times acceleration, the idea is that once you've got an object instantiating the universal of having a particular mass and instantiating the universal of having a certain force acting on it and take the universal of accelerating at a certain rate...

Those three universals are kind of glued together by this relation of what's sometimes known as natural necessity, such that any object that's instantiating the first two universals is guaranteed to instantiate the third universal. Now, whether you think that that's kind of mysterious and magical is an open question. Obviously, Armstrong doesn't. Humians in general are very suspicious about the notion of natural necessity. They do kind of think that this is a bit of metaphysical hocus-pocus that we should do without. Is that the only candidate for explaining what a natural law is?

Well, aside from the Humean, this is just a bunch of regularities kind of view, there's a third line of thought that's become popular in the last few years, which goes by the name of dispositional essentialism, which is a bit of a mouthful. So if you go back to Armstrong again and his relations of natural necessitation, the thought is that you have these universals, these repeatable features that objects have, but they're having those features just in itself as

doesn't entail anything about how they're going to behave. In principle, you could imagine a universe where objects have just the same sorts of physical properties as in the actual world, but behave in completely different ways. Things go up rather than down when you drop them, or things obey an inverse cube law rather than an inverse square law, or whatever it is.

So the fundamental features of things just by themselves don't guarantee how they're going to behave. You need to add in the relations of natural necessity before you get to infer facts about what they're actually going to do. And those relations of natural necessity hold in the actual world, but they might not hold in some other possible world. Now, what dispositional essentialists say is...

That picture of the nature of the fundamental features of things is mistaken. If you think about the fundamental features that objects have, they're really dispositional features. You can think of a disposition as things like fragility. I mean, these are not going to be really fundamental physical properties, but just kind of by analogy, when you say that a glass is fragile,

you're saying something about how it's going to behave in certain kinds of situations, right? If I say, oh, be careful, that glass is fragile, you know that I'm telling you not to drop it on the floor or to dry it very carefully or whatever it is, because to be fragile is to be disposed to break in certain kinds of situations. Similarly, take a property like mass, which maybe does deserve to be thought of as a fundamental property. The dispositionist will say that

To have mass is to be disposed to behave in certain kinds of ways in certain kinds of situations. It's not, as it were, a property that's separable from the way the object behaves in principle, so that you could take that property and now imagine that something had that very same property and yet behave in different kinds of ways.

So now what the dispositional essentialist says is, look, the fundamental properties of objects are dispositions. And now once we've got that claim, that the fundamental properties are dispositions, we've already done all the work that laws of nature were there to do. We don't need this extra law of nature to kind of come in and get in on the act and do some work. Could I just take you back to that example of the fragile glass? What would the two non-Humian accounts that we've thought about so far say about that case of the glass that might break?

What the defender of the Armstrongian necessitarian view is going to say is, look, fragility isn't really a fundamental property. What underlies the fragility of the glass is the fact that the glass has a certain kind of microstructure...

And it's a law of nature that things that have that kind of microstructure, when they come into contact with hard surfaces, shatter. But just the fact that the glass has that microstructure and the floor is hard just by themselves, that doesn't guarantee anything about the glass is going to behave. You could imagine a world where glasses with just the same kind of microstructure got dropped on hard floors and nothing bad happened. The glass just kind of bounced up. The laws of nature would have to be different, but that's perfectly conceivable.

So on the Armstrongian view, we have to now think that there's a necessary connection between what's happening with the microstructure of the glass when it comes into contact with a very hard surface. That's an extra fact, as it were, about the relationship between those two things.

Now, the dispositional essentialist view... I mean, the dispositional essentialist actually agrees in the case of fragility because they don't think that fragility is a fundamental property. But let's imagine that fragility is a fundamental property. The thought is that the very fact that the glass is fragile, the fact that that's a disposition to break in certain kinds of circumstances, once you know that the glass has that disposition...

you know that the glass is going to break. A fragile glass couldn't help but break, right? Trying to imagine a possible world now where you have a fragile glass that doesn't break when you drop it on a hard surface, you can't do it, I mean, unless you imagine it being encased in bubble wrap or something. In exactly the same circumstances, if the glass is fragile, it's guaranteed to break. So you don't need this extra...

as it were, necessary connection to tie those two things together. It's just given by the fact that the glass has that property that it must break. I guess what we've been doing is focusing on the nature of reality and the two sorts of theories you've been talking about. People have been trying to explain what's going on when we or anyone postulates a law of nature. But do we really need laws of nature in the first place? I mean, couldn't we get by with just saying this is something that seems to hold, it works very well for us, it's pragmatically useful?

Well, I think up to a point it does matter. So, for example, we engage in counterfactual reasoning all the time. I might want to know what would happen if I put my foot on the brake pedal or steered round to the right, even if I'm not going to do that. Or if you're working in a nuclear power station, it might be extremely important to know what would happen were you to press the big red button that says do not press. And it looks like we need to invoke laws of nature when we ask those sorts of questions. When we try and answer them, we hold certain facts about the world fixed and vary other kinds of

facts. So for example when I wonder what would happen if I dropped my pen I don't hold fixed the fact that all the pens in this room are more than three feet off the air right that would get me to the silly answer that the pen would float in the air were I to let it go. The things that I want to hold fixed by and large are the laws of nature so I want to hold fixed the law of gravity and not the mere accident that all the pens in the room are more than three feet off the ground otherwise I'm clearly going to get the wrong answer.

We need to give some kind of an account of why it is that the laws of nature are the sorts of things that we hold fixed when we engage in counterfactual reasoning, whereas the accidental generalisations we don't hold fixed. But now the question is whether we really need to invoke the kind of metaphysical accounts of laws that the Armstrongian invokes or the dispositionalist invokes in order to be able to do that kind of thing. And I guess my view is that we don't need to invoke those sorts of heavy-duty metaphysical accounts if we think of the laws of nature as just...

the axioms in our best system, so a certain very important subset of the regularities, then, as it were, their status as axioms is what's driving the thought that we hold them fixed when we do our counterfactual reasoning. You hold the axioms fixed and you let the other stuff vary. So that's a very metaphysically neutral account. We're not postulating any extra ontology, any extra kind of population in the world in order to account for the work that the laws of nature need to do. The laws of nature just are the principles...

that we hold fixed when we reason about the nature of reality or what's going to happen in certain sorts of situations, as opposed to no human being ever lives to the age of 125 or whatever it is. Who knows whether that claim is true, but even if it does turn out to be true,

It's not the sort of thing that one ought to hold fixed when one's engaging in counterfactual reasoning. If someone was coming up to their 125th birthday, it would be kind of mean, but also mistaken to say, ah, nobody lives to their 125th birthday, sorry, you know, you've got another three hours and that's going to be it. Whereas if someone's proposing to jump off the Eiffel Tower, you probably would be wise to point out to them that it's no accident that people who jump off the Eiffel Tower come to a very sticky end.

In Jean-Paul Sartre's novel Nausea, the central character starts almost going crazy thinking about everything that might happen. Once he's got this notion of humian contingency, he thinks, well, look, maybe our tongues are going to turn to centipedes. You can't really be absolutely sure that won't happen. Is that the position we end up with with your line? Well, yes. We have to be a little bit careful in that.

not assuming that the alternative positions don't leave us in a precarious position. So if you believe in natural necessity, it's all very well believing in this timeless connection that kind of glues everything together. But of course, you might say, well, why should we believe in this timeless connection? What stops us thinking that that necessary connection will just stop holding tomorrow? So there's a sense in which the necessitarian isn't in a much better position. Nonetheless, I think the humane position does enshrine a kind of

of conception of the universe as a kind of fundamentally precarious place. The fact that the universe happens, things tick along in this nice regular way, just is a brute fact about the universe. There's no explanation for why that should be the case. We're just extremely lucky that things do work in that way and we all have to cross our fingers and hope that things carry on happening in a nice regular way. Helen Beebe, thank you very much. Thank you.

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