ABSTRACT
One of the reasons that have led us, in the preceding chapter, to pro-
pose an account of the concept of a law of nature opposed to more traditional accounts is the following: we have begun by observing that a law,
even if it is valid, may have exceptions. By an exception I mean a situation
in which, to take the simplest case of a law whose form is that of an
implication between two properties, the antecedent property is exempli-
fied but not the consequent property. In this chapter I shall try to justify
the hypothesis already introduced in the last chapter, that the validity of a
law does not guarantee the universal exemplification of the consequent in
all cases in which the antecedent is exemplified. The validity of a law (L) is not sufficient for the truth of the corresponding universal gen-
eralization (U).
