component
Ross uses this word in a fairly narrow and technical sense to draw some significant distinctions. “Components” are indispensible features of what a thing is, but not every feature of the thing in its material instantiation qualifies as a “component,” which is actually why you are able to have more than one (material) instantiation of the same nature. Those material features which are not components are nevertheless necessary for the existence of the thing, but do not constitute an indispensible component of the nature. Ross refers to them as “overflow” necessities, precisely because they overflow the boundaries of the nature they instantiate. For example, if you have two lions, they will behave in similar ways and have similar DNA, but they won’t share the same molecules. The individual molecules that make up a lion do not enter, as individuals, into what it means to be a “lion,” but they are definitely necessary for the existence of a lion, and they have a life of their own, as it were. Some of operative physical dynamics that occur within a lion depend on the nature of the molecules themselves, and not on the nature of lions. (It is worth noting that Ross’s definition of natures is similar to the modern notion of a “dynamic system”).
The fact that the necessities that are the building blocks of a nature overflow the nature is a key source of erroneous judgment:
T&W: As Chap. 8 indicates, the imagination lures one towards falsity, because the de re necessities of a thing are not all [do not all count as] components of what it is.
If what a thing is is entirely exhausted by its components (with no reference to overflow necessities), then it is a “resultant“.
Every resultant is clearly traceable in its components, because [components] are homogeneous and commensurable.
In fact, this is what distinguishes a “resultant” thing from an “emergent” thing.
It is otherwise with emergents, when, instead of adding measurable motion to measurable motion, or things of one kind to other individuals of their kind, there is a co-operation of things of unlike kinds. The emergent is unlike its components insofar as these are incommensurable, and it cannot be reduced to their sum or their difference