 Most of the work will be done by the applicability criterion. We must say more (as Salmon indeed does) about what sort of a guide to life probability is supposed to be. Mass, length, area and volume are all useful concepts, and they are ‘guides to life’ in various ways (think how critical distance judgments can be to survival); moreover, they are admissible and ascertainable, so presumably it is the applicability criterion that will rule them out. Perhaps it is best to think of applicability as a cluster of criteria, each of which is supposed to capture something of probability’s distinctive conceptual roles; moreover, we should not require that all of them be met by a given interpretation. They include: