This is what I'm asking. Is the idea of "cat" in my mind different from a particular cat? Is it a generalization drawn from my experience of little fuzzy creatures that I've observed? If so, how can my idea of "cat" be the same as your idea of "cat," since we have observed different fuzzy creatures? And does the idea correspond to any reality, since things we've labeled "cats" are merely apparently similar creatures in the process of evolution.
The problem:
For Hume, Stuart Mill, Spencer, and Taine there is strictly speaking no universal concept. The notion, to which we lend universality, is only a collection of individual perceptions, a collective sensation, "un nom compris" (Taine), "a term in habitual association with many other particular ideas" (Hume), "un savoir potentiel emmagasiné" (Ribot). The problem of the correspondence of the concept to reality is thus at once solved, or rather it is suppressed and replaced by the psychological question: What is the origin of the illusion that induces us to attribute a distinct nature to the general concept, though the latter is only an elaborated sensation?...Nominalism, which is irreconcilable with a spiritualistic philosophy and for that very reason with scholasticism as well, presupposes the ideological theory that the abstract concept does not differ essentially from sensation, of which it is only a transformation. The Nominalism of Hume, Stuart Mill, Spencer, Huxley, and Taine is of no greater value than their ideology. They confound essentially distinct logical operations--the simple decomposition of sensible or empirical representations with abstraction properly so called and sensible analogy with the process of universalization. The Aristotleans recognize both of these mental operations, but they distinguish carefully between them.
The solution:
[Moderate Realism] reconciles the characteristics of external objects (particularity) with those of our intellectual representations (universality), and explains why science, though made up of abstract notions, is valid for the world of reality. To understand this it suffices to grasp the real meaning of abstraction. When the mind apprehends the essence of a thing [the species] (quod quid est; tò tí en eînai), the external object is perceived without the particular notes [accidents] which attach to it in nature (esse in singularibus), and it is not yet marked with the attribute of generality which reflection will bestow on it (esse in intellectu). The abstract reality is apprehended with perfect indifference as regards both the individual state without and the universal state within: abstrahit ab utroque esse, secundum quam considerationem considerattur natura lapidis vel cujus cumque alterius, quantum ad ea tantum quæ per se competunt illi naturæ (St Tomas, "Quodlibeta", Q. i, a. 1). Now, what is thus conceived in the absolute state (absolute considerando) is nothing else than the reality incarnate in any give individual: in truth, the reality, represented in my concept of man, is in Socrates or in Plato. There is nothing in the abstract concept that is not applicable to every individual; if the abstract concept is inadequate, because it does not contain the singular notes of each being, it is none the less faithful, or at least its abstract character does not prevent it from corresponding faithfully to the objects existing in nature. As to the universal form of the concept, a moment's consideration shows that it is subsequent to the abstraction and is the fruit of reflection: "ratio speciei accidit naturæ humanæ". Whence it follows that the universality of the concept as such is the work purely of the intellect: "unde intellectus est qui facit universalitatem in rebus" (St. Thomas, "De ente et essentia," iv).
Wow. You write like any of a number of philosophy majors I knew when I was getting my engineering degree. Always trying to come up with reasons to confuse the simple.
What do I mean by "cat?" Well, if I say "cat," and don't qualify it further (say, by mentioning bobcat, lions, tigers, etc.), I mean a common house cat. Species Felis, Genus Catus. What breed is irrelevant. if it can breed with a Felis Catus and have offspring which are fertile, then it's a Felis Catus, common housecat.
Any discussion beyond that is meaningless Liberal Arts crap.
> The problem: For Hume, Stuart Mill, Spencer, and Taine there is strictly speaking no universal concept.
That's *their* problem. Most of the rest of humanity is able to get along just fine, and more or less perfectly understand the people they communicate with. I leave it to philosophers to waste their lives navel-gazing and wondering at the whichness of the why.