Laws, Explanation, Prediction, and Understanding

Abstract

A law, i.e., a scientific law of nature, may be defined as a statement describing a regularity of events or characteristics [see, e.g., Walters (1967) who also discusses other views]. Thus, a law refers to a pattern which, according to our experience, is invariant; invariant may mean universally invariant. A number of more detailed definitions of the concept of law have been proposed (see, e.g., Ruse 1970), and different types of laws have been distinguished, such as, for example, deterministic and probabilistic laws. A deterministic law [which Hempel (1966) calls a ‘universal law’] is a statement which says that “whenever and wherever conditions of a specified kind F occur, then so will, always and without exception, certain conditions of another kind, G” (Hempel 1966, p. 54). In short: when F, then G. Although this definition of a deterministic (or universal) law may appear satisfactory at first sight, it raises problems for several reasons (see, e.g., Walters 1967). One of these problems is that it is also true for accidental (or descriptive) generalizations which are not laws. An example of an accidental generalization is the statement: all apples in this basket are red. Evidently this statement is not a law; however, it satisfies the above definition: when F, then G - F being the condition of being an apple in the basket, and G the condition of being red. Thus the characterization: when F, then G, is a necessary but not a sufficient condition for the definition of deterministic laws.