James Ladyman is Professor of Philosophy at the University of Bristol. His work has predominately focused on the philosophy of science and mathematics. He is co-editor of the collection Arguing About Science, an introduction to the essential topics in the philosophy of science.

What do we mean by “cause and effect”?

Well, that's very contentious. I'm not quite sure how to answer that. I think, traditionally, a cause is thought to be a sufficient condition for an effect, but that’s if the cause definitely happened.

That's not what people tend to think now. They tend to think there are various causal factors; causation might be probabilistic, it might be all or nothing. I think cause and effect has been blown wide open as science has changed. For one thing, there are all sorts of diverse uses of cause and effect. Adaptation being caused by natural selection, for example, is the kind of causation that can only happen at population level.

But people might say, "smoking causes cancer”. They might be largely talking about population level effect, even though they also think that for any given individual there's a singular causal story. Someone might therefore smoke and have cancer without smoking being the cause.

So it's a little different to the traditional picture of an almost mechanistic idea of “cause and effect”?

All or nothing, you know.

How has quantum mechanics challenged our understanding of cause and effect?

By suggesting that there may not be determinants. So it’s made us think that the world might be fundamentally probabilistic. I’m not saying that’s right, but that’s certainly what it’s made us worry about.

Do you think that something like quantum field theory has changed the idea of forces, and whether there's something perhaps more fundamental driving the universe?