see discussion of eidos in transcendent / immanent
John Locke distinguished between the "nominal essence" and the "real essence." The nominal essence is that set of properties whose manifestation is necessary for a thing to be identified as of a certain kind, in order to name the thing. The real essence is the nature of the thing, conceived as the "hidden" structure which causally accounts for its manifest properties and provides the choice of criteria for individuation and identity.
For revisionist Biologists like Brian Goodwin and Gerry Webster, the organism and its parts must be thought as "powerful particulars." If their real essence is to be equated with the causal mechanisms responsible for the production of manifest morphological characteristics, this essence must be sought in the morphologically relevant structure of the organism and its parts.
what is "eidetic thinking" ? (see geometry for "eidetic sciences")