UFO.UFO-A
Class Rigid Sortal

UFO.UFO-A.Rigid Sortal

Direct Known Subclasses:

Subkind, Substance Sortal

public class Rigid Sortal

A universal U is rigid if for every instance x of U, x is necessarily (in the modal sense) an instance of U. In other words, if x instantiates U in a given world w, then x must instantiate U in every possible world w’.