ABSTRACT
The notion of a law of nature is fundamental to science. In one sense this is obvious, in that much of science is concerned with the discovery of laws (which are often named after their discoverers-hence Boyle’s law, Newton’s laws, Ostwald’s law, Mendel’s laws, and so on). If this were the only way in which laws are important, then their claim to be fundamental would be weak. After all, science concerns itself with much more than just the uncovering of laws. Explaining, categorizing, detecting causes, measuring, and predicting are other aims of scientific activity, each quite distinct from law-detecting. A claim of this book is that laws are important because each of these activities depends on the existence of laws. For example, take Henry Cavendish’s attempt to measure the gravitational constant G using the torsion balance. If you were to have asked him what this constant is, he would have told you that it is the ratio of the gravitational force between two objects and the product of their masses divided by the square of their separation. If you were then to ask why this ratio is constant, then the answer would be that it is a law of nature that it is so. If there were no law of gravitation, then there would be no gravitational constant; and if there were no gravitational constant there would be nothing that counts as the measurement of that constant. So the existence and nature of a law was essential to Cavendish’s measuring activities. Somewhat contentiously, I think that the notion of explanation similarly depends upon that of law, and even more contentiously I think that causes are also dependent on laws. A defence of these views must wait until the next chapter. I hope it is clear already that laws are important, a fact which can be seen by considering that if there were no laws at all the world would be an intrinsically chaotic and random place in which science would be impossible. (That is assuming that a world without laws could exist-which I am inclined to think doubtful, since to be any sort of thing is to be subject to some laws.) Therefore, in this chapter we will consider the question: What is a law of nature? Upon our answer, much that follows will depend.
