I am continuing the discussion of realism and nominalism. Here I make the distinction between genera (genus-species relationships), generals (e.g., Lockean abstractive processes), and universals. I also explain the importance difference between a realist and nominalist on several key points of metaphysics and phenomenology.
Leon and I were discussing the basics of Duns Scotus, etc., and my own appropriations of the terms that adds some Aquinas. Below is an edited portion of our discussion.
The terms are “real distinction,” “formal distinction,” and a third term I do not know off the top of my head. We often just say a “mere distinction" or "merely formal."
Universals and genera are of the second kind. I forgot what the perfections are, which are special cases of this ontological problem. Note that genera and generals are distinct, whereas the latter refer to principles arrived at via an inductive process, e.g., Locke’s “abstraction” or logical induction. The former refer to genus-species relationships, e.g., categorical logic.
Correct, generality (generals) is neither a real nor formal distinction. Hence, a nominalist often thinks that generality is all we have—not universality or genera of being.
As for essence vs. thing, you are right. If we are Hobbes-style nominalists and think that all things are (corpuscular) particularities, then we deny essences. Recall that essences are a kind of universal, while quality is another kind of universal. Also, "essentiality" is not the category of uniquity (uniqueness); the latter is "quiddity." As I wrote in my post, nominalism gives up on substantial or essential identity—identity is a best a function of something. It does not necessarily give up on absolute particularity.
As for whiteness, it is a universal and a general, but not in the same way for both. Insomuch as whiteness has reality, it is a universal. Insomuch as we experience or know whiteness, it is a general; we infer from experience that this encounter is of the category of whiteness. Now, if we are not realists about universals, then we know merely the generality “whiteness.” The problem here is that we no longer experience the real thing, but merely a generated appearance. If one is a nominalist, one does not think that there is anything “under” this generation.
In my Peirce-Deweyan position, for instance, we add to the idea that whiteness is a universal and general. We talk about the generation of the phenomenal quality, so we are talking about a generated quality. However, since we think that generation is a real process, then the generated quality maintains a real, non-arbitrary relation to the thing experienced. (Note that the “thing experienced” is not an entity or object, but I’m keeping it simple for now.) A nominalist, on the other hand, can merely say that the phenomenal quality was generated, full stop.