Abstract

In empirical science, hypostatic abstraction posits an entity defined by its assumed physical relation to a known phenomenon. If the assumed relation is real, the posited entity is physically real and is not an ens rationis. The posited entity, being identified indirectly, by its relation to something else, may be the agreed-upon subject of mutually incommensurable theories, and this is a key to understanding the history of science. Natural kinds may be introduced by hypostatic abstraction, and this explains why, contrary to received doctrine, concepts of natural kinds can never be vague in the sense of being fuzzy, though they can be vague in the sense of lacking specificity. Terms defined by hypostatic abstraction are rigid designators in Kripke's sense, but show how rigid designation is consistent with the Fregean theory of reference.