Two types of realizable-entity definitions

[michaelrabenberg]

Consider these definitions:

Language Skill. A Skill that is realized by an Act which is prescribed by a Language.

Electromagnetic Radiation Property. A Disposition that inheres in an [sic] bearer in virtue of how that bearer interacts with electromagnetic radiation.

Definitions of realizable entities overwhelmingly fall into one or the other of two categories, which we might call realization-based definitions and grounds-based definitions. The Language Skill definition is an example of a realization-based definition; it defines a Language Skill as a Skill with a certain sort of realization. The Electromagnetic Radiation Property definition is an example of a grounds-based definition; it defines an ERG as a disposition that inheres in its bearer in virtue of such-and-such fact.

Some definitions are both realization-based and grounds-based. Consider, for example, this one:

Surface Tension. A Disposition that inheres in a liquid and is realized when the cohesive forces of the molecules in the bearer at the surface are greater than the adhesive forces of the molecules in the surrounding air.

Realization-based and grounds-based definitions are very different types of definitions. One says that what it is to be something is (crudely) to behave in a certain way; the other says that what it is to be something is to have a certain source. I'd be interested in whether anyone thinks there might be principled reasons to define certain types of realizable entities in one way and certain other types of realizable entities in the other, which would justify the definitional differences, or whether there might be reasons to try to move toward more uniformity among the definitions.