If you ask the average man on the street what a law of nature is, chances are you’re going to get a reply that’s not too dissimilar from what Nancy Cartwright calls the ‘facticity’ view – ‘the view that laws of nature describe facts about reality.’ (Do the Laws of Physics State the Facts?) Cartwright describes this view as so deeply ingrained into the (presumably human) psyche that it doesn’t even have a name. It is simply The View. Comparing the laws of physics with biological laws, Cartwright notes:
The fundamental laws of physics, by contrast, do not tell what the objects in their domain do. If we try to think of them in this way, they are simply false, not only false but deemed false by the very theory that maintains them. But if physics’ basic, explanatory laws do not describe how things behave, what do they do? Once we have given up facticity, I don’t know what to say. (Do the Laws of Physics State the Facts?)
Cartwright herself is an anti-realist about the laws of nature, and denies this View. The LoN, she claims, founder on a dilemma: either laws are false but have explanatory power, or they are true but have no explanatory power. This is an interesting dilemma, for a couple of reasons. It’s deeply counterintuitive, to be sure. Is it, however, itself false? I don’t know for sure if it’s false, but I do think that what it gets at has enough force to show that to be a realist about the laws of nature rules out what is commonly called the ‘regularity theory’. Cartwright arrives at her conclusion via a study of gravitational and electrostatic attraction/repulsion:
Much of Cartwright’s case against fundamental laws rests on her illustration involving the laws of gravitational and electrostatic attraction (and repulsion). If the gravitational law were true, then it would describe how bodies behave. In particular the law would predict the real, actual forces that act on gravitating bodies. But nearly all gravitating bodies are also electrically charged, and the smaller the body, the greater the role that charge plays in determining its behaviour. Thus, taken at face value, the gravitational law seems false; it does not state correctly the actual net force acting on all gravitating bodies because the actual net force experienced by most bodies depends jointly on their mass and electrical charge. (Philosophy of Science: The Central Issues, p. 89)
The key point here is roughly this: either the law is blatantly false, or the law describe the behaviour of bodies in conditions that rarely obtain; so rarely, in fact, that the explanatory power of the law, if true, is almost nothing. Crucial here is Cartwright’s insistence that part of the problem is thinking of laws (on the Facticity view) as mono-causal: they are concerned with giving a true description of one and only one cause, and the problems arise when this view is taken to try and describe an event when several causes are at work. As she insists, ‘There aren’t two vehicles for explanation – laws for the rare occasions when causes occur separately; and another secret, nameless device for when they occur in combination’. Thus the route is closed for realists about laws of nature. Cartwright’s own constructive proposal, however, is interesting, because in its anti-realism, it opens up a new door to the realist.
Cartwright’s own proposal is dispositionalist in character; that is, laws of nature are ‘about’ the powers, tendencies or dispositions of things in the world:
In the real world, according to dispositionalists, there are huge numbers of tendencies and powers in acting simultaneously in open systems, the joint upshot of which is what we observe. Experimental procedures, by creating closed systems, enable investigators to isolate tendencies and study their effects when acting singly. In nature there are no closed systems. Our Laws of Nature, abstracted from the real processes in open systems, are true, not of the world, but only of abstract and simplified models of aspects of that world. (Rom Harré, A Companion to the Philosophy of Science, p. 218)
Right off the bat we can see why a dispositionalist wouldn’t take the laws of nature to be true descriptions of bodies in the world, and Cartwright’s dilemma only reinforces this. What this dispositionalist position does, however, is show that any realist about the laws of nature will in all likelihood need (or at least be open to the possibility of) an account of natural laws that is based on essence. If Cartwright’s anti-realism about laws of nature has any force – and it does – the only option for realists is going to be a dispositionalist account (powers, tendencies, etc). This probably requires at least some kind of account of essences, essential properties and natural kinds, because it’s only from an account of essences that an account of dispositions and powers can get the force it needs.