What Are the Laws of Nature?

This is the weekly Q & A blog post by our Research Professor in Philosophy, Dr. William Lane Craig.

Question

I am writing with a question regarding the nature of the laws of physics. I heard it said recently that the laws of nature are not “things”. The claim, made by a theist, was that the Humean view of the laws of nature was the most plausible. Now I agree with him in a sense in that these are not “laws” per se. They are more like regularities or descriptions of what would normally happen under ideal circumstances. My issue is that it seems unusual to say the laws of nature aren’t “things”. Is that to say they don’t refer to anything?

Pruss has discussed this issue and made an interesting point, which makes sense, that “if p is a purely categorical proposition that is a law of nature, then we can ask not just what the truthmaker of p is, but also what is the truthmaker of the further proposition that p is a law of nature. This truthmaker must be some aspect of reality. It must thus exist…” He then goes on to argue that the laws of nature are Aristotelian Forms. However I am not sure about this either. I would greatly appreciate your own learned perspective on the matter. Thank you!

P.S. Please come to Vancouver, BC someday soon.

Alex

Canada

Dr. William Lane Craig's Response

I can’t believe you asked this question, Alex! I just returned from a conference on divine action at Trinity Evangelical Divinity School last week, where my friend and colleague Paul Gould and I were tasked with responding to a paper by philosopher of science Jeff Koperski entitled “The Nature of the Laws of Nature.” Your question gives me the opportunity to share a bit of what I said there.

The central question of Jeff’s paper, which he says all sides in the debate over the nature of the natural laws are trying to answer, is the following: “What ultimately accounts for changes of state that occur within systems according to fixed regularities?” In addition to Hume’s approach, which reduces natural laws to either mere regularities between events or statements about those events, Koperski says that non-Humeans have historically favored one of two replies: The first is that the causal powers/capacities of physical entities enable them to do such-and-such and so account for regular change.  The second reply is to appeal to the laws themselves. They are what ensure that a system will progress from one state to the next in a predictable fashion.  Jeff says that both responses share a common intuition: “There must be something that moves systems from one state to the next in regular ways, if not causal powers then laws.”

The second reply seems to me confused. Natural laws (as Pruss discerns) are either true or false. Whether natural laws are expressed as mathematical equations or as prose sentences, in either case, even if we grant positive ontological status to natural laws, they are not the sort of thing that can have an effect upon physical states of affairs. For whether natural laws just are mathematical equations or propositions expressed by prose sentences, they are abstract entities. But abstract entities are causally effete; they have no effect upon anything. That’s part of what it means to say that something is abstract.  They cannot come into contact with physical objects and are not agents endowed with causal powers. Thus, natural law cannot fill the office of efficient causation that moves a system from one state to another. The laws, if true, can accurately describe such a transition or enable us to predict that transition, but they cannot explain it.

I myself, as an anti-Platonist, one who rejects the existence of abstract objects, don’t think that natural laws exist in a metaphysically heavy sense. When we speak of laws of nature this is but a useful façon de parler for talking about how the physical world operates. If we were to draw up an ontological inventory of all the things that exist, it is not as though we should have to include in our list, in addition to God and the things in the physical world, the laws of nature. Natural laws, it seems to me, are just codifications of how the world works.

Now that gives me a certain affinity and sympathy with the Humean, in that he, too, ascribes no positive ontological status to natural laws. But regarding the laws of nature as mere regularities of nature fails to answer our question of whyregular changes of state occur in physical systems. In other words, we want some explanation of why the laws of nature contingently describe our world. Various universes operating according to different laws of nature could have been real. So why is the universe governed by these laws? The reason that philosophers might want to appeal to causal powers is that the laws of nature contingently apply to the physical world. An account which explains why the laws of nature obtain has greater explanatory depth than one which just says, “That’s the way it is.” That last answer may be just fine for the scientist who is exploring the universe that does exist; but we’re asking about a philosopher who asks deeper questions about why the world explored by the natural scientist operates according to the laws that it does.

I think this is what Pruss is expressing in his rather recondite way in asking “What is the truthmaker of the further proposition that p is a law of nature.” 

I think that what explains why certain laws are true rather than others is the causal powers which physical things possess. So I find the first reply to be the better answer. Now as a theist, I’d prefer a theistic version of the first reply: God created various entities with different causal powers. But beware: It’s not as though causal powers are metaphysically heavyweight objects which are instantiated in physical things. It’s just that God creates physical entities which can do different things. That’s the difference between my preferred answer and Pruss’ more metaphysical answer that appeals to mysterious entities like immanent Aristotelian forms in things.

The deeper issue here is a meta-ontological question: What determines one’s ontological commitments? Since W.V. O. Quine, a very popular answer has been that we are committed ontologically to things we refer to and say there are in sentences we take to be true. The burden of my work on God and abstract objects, such as God over All, is that the neo-Quinean criterion of ontological commitment is disastrously wrong (or, more modestly, there’s no good reason to assume its truth). So if I say something like “Physical things have different causal powers/capacities,” I’m not committing myself to recherché objects like powers or capacities that are somehow immanent in things. Talk of powers, capacities, and dispositions is, like talk of natural laws themselves, but a façon de parler which is metaphysically light. That is a view which should appeal to your theistic friend.

This Q&A and other resources are available on Dr. William Lane Craig's website.