Abstract

Natural necessity is analyzed in terms of “sub-nomic stability” (introduced in Chapter 1). The various species of necessity correspond to the various nonmaximal sets possessing sub-nomic stability. This approach explains what natural necessity has in common with other varieties of necessity by virtue of which they all qualify as varieties of the same thing. Necessities relative to some arbitrary class of facts (merely relative necessities) are thereby distinguished from genuine varieties of necessity (contrary to David Lewis's account of “must”). Different strata of natural law possess different grades of natural necessity. This approach explains what makes one variety of necessity “stronger” than another. Indeed, this approach explains why all varieties of necessity have characteristic places in a single, well-defined ordering from strongest to weakest. It is thus shown how natural laws can be genuinely necessary despite being contingent.