The man is pleased with your request; he happily returns to his speech on horses and particular existence. As he does so, he brings you over to another display case. Inside is a diagramme of the metaphysical kingdom of horses. It is a colourful array that constitutes an interrelated whole, with each region enjoying some meaningful relationship to every other region.
Let's revisit the topic of "horse" in its most broad and general sense. Does "horse" refer to all of the horses? Yes, but it's also broader and more complex than one might expect. If you round up horses you will have a herd, but that is more limited than the meaning we wish to express. "Horse" encompasses the horses in the field and the horses in your mind's eye, as well as so much more.
The general term "horse" captures all of it, including the horse in your mind's eye and the horses who live at our stables. It also goes beyond that and captures the relationships between these particulars, and to a more limited degree their relationships with everything else in reality. It will ultimately constitute an intelligible unity; if we plot it out we will see the complete domain of horses and their existential network.
But given that we might use a definition of "horse" that is broader or narrower, is "horse" real? The answer is that we were never discussing how to pin down a free-floating word, that is just a semantic game. Instead, we are identifying regions of existence. That which is referred to by the term "horse" is real regardless of where you draw the lines, so long as it identifies a unified, intelligible segment of Being, such that to tear it apart would lose some information.
Similarly, particular horses are real because each one represents something beyond its constituent parts. There are the various substances that go into the horse in question, they are arranged in a particular way within a particular context, and they have a complex set of internal and external relationships. The specific horse being signified is a coherent and unified whole; there is a necessary commonality that pervades the distinctions and must be captured.
That we could narrow the scope and identify each of its legs does not change anything about whether the horse is real. The legs are real, but in narrowing our focus we lose their relationship to each other and everything else. Just as "horse" encompassed the horses and captured their unity and presence in Being, the particular horse does so to whatever body-parts we might examine.
Finally, some might ask whether the relationships are not themselves a constituent part of the horse. If that is the case, a horse really does boil down to a collection of parts with no loss of meaning; you could separate each leg and each relationship and consider each thing independently. This explicit account of the process reveals the problem: the relationships cannot be preserved without the presence of the legs; we cannot sunder them without loss of meaning. Indeed, if we subjected a leg to the same treatment as the horse, we would lose the meaning of the leg and be left with a mysterious pile of flesh and bone. Those pieces, too, will themselves be unified wholes that are subject to the same issue. Meaning is whole all the way down.
The relationships cannot be forgotten, they have significance and therefore ontological presence. To cut them out of the picture and destroy unity is to exclude information and meaning. Therefore, horses and their broader, metaphysical kingdom remain secure and must be respected.
The man nods, satisfied with his speech.