Scientific Laws

Abstract

Scientists and others often use phrases such as ‘natural law’, physical postulate’, ‘fundamental principle’ ‘NN’s law’, ‘NN’s equation’ etc. The things denoted by these phrases are often referred to as ‘laws of nature’ in the philosophical debate. The core problem is how to distinguish between laws and accidental generalisations.

Philosophers disagree sharply about the concept of a law of nature. Some say that it is obvious that there is a certain category of propositions, laws, which differ from other true propositions of the same logical form, accidental generalisations. Many of these philosophers think that the property of being a law is based on a kind of metaphysical necessity. Other philosophers of a more empiricist bent disagree and point out that the predictive power of a theory does not depend on whether some of its propositions are called laws or not; calling some true propositions ‘laws’ is unnecessary metaphysics. This empiricist argument is convincing, but why, then, is the concept of natural law, used not only by philosophers but also by laymen and scientists? Surely, this concept serves some purpose, although perhaps not a philosophical one.

For four types of laws it is possible to give an explanation of our propensity to call them ‘laws’ and treat them as having a special status of being physically necessary, without assuming any kind of metaphysical necessity. The first type comprises conservation laws, each of which can be shown to be a consequence of a certain objectivity demand on our descriptions of the events in nature using Noether’s theorem. The second type comprises some equations, each of which may be viewed as an implicit definition and at the same time an empirical generalisation of observations. The third type consists of explicit definitions of one of the quantities used in the respective equation. Finally, those true generalised conditionals that can be derived from the two types above are also labelled laws.

Saying about a law that it is necessary is analysed as short for ‘necessarily true’ which in turn is interpreted as a semantic predicate, not as a sentence operator. Hence modal logic is not applicable to law statements.

Nature and Nature’s laws lay hid in night

God said ‘Let Newton be!’ and there was light

A Pope