But what are the limits of the internal relations theory? It can't be applied to relations between abstract universals, such as the relation of equality between the pure number 4 and 2 + 2. And this is because we can't talk about the possibility of an abstract universal being different from what it is, but only to relations between concrete terms.
That's true in a sense. If an abstract universal means an abstracted universal, which is a universal considered separately from its context in nature, then it will not depend on its relations because we have defined it that way.
But using universals as if they were independent does not prove whether they are independent. My argument is that they are not independent as they exist in nature.
So in a sense the internal relations theory applies only to concrete terms. It applies only to things, attributes and relations taken in the natural or original situation, although this does not necessarily mean that the entire concrete context has to be exhausted before the internality is apparent. The theory does not apply to objects taken in that abstraction which would beg the question, but in their real or natural habitat.
We mentioned being red-headed because it's trivial. The attribute at first seems so clearly 'external' to its subject that it makes the issue extremely difficult. Hence, it's a crucial instance for the theory of internal relations.
If you could have a perfect relational knowledge of the total, you could go from the nature of red-headedness to these other characters which qualify it, and from the nature of red-headedness you could reconstruct all the red-haired people. With this perfect knowledge you could start internally from any one character in the universe, and pass to all the other characters. In each case you would go more or less directly or indirectly, and with unimportant characters the amount of indirectness would be enormous, but no passage would be external.
Such knowledge is out of our reach, and possibly out of the reach of any mind that has to think relationally. But if knowledge is perfected in the Absolute, as we believe, then the purpose of such knowledge is realized in a higher form, and along with ignorance and chance, the last trace of externality has vanished.