This point has perplexed a number of communities: in many places they failed to distinguish between the one and the other, even though the distinction is manifest. They went on speaking with the word “one,” imagining that it meant numerical identity, whereas it denotes only unity of kind. Hence the maxim, “Most of the disagreements among rational people arise from the overlap of names.” Matters finally reached the stage where certain groups—claiming true insight, tawḥīd, and decisive discrimination, and asserting that they have unveiled the knowledge to which Hermes of the primordial ages merely alluded, and which, they say, the Prophetic guidance sought to convey—ended up declaring existence to be one in this sense, on the ground that all existents share the designation “existence.”

There is no doubt that the things which exist do share the name “existence,” and that existence is one in that regard. Yet there is a difference between what is one in concrete reality and individuality, and what is one in species, genus, or common predicate and the like in the terminology of the logicians—all of which the grammarians gather under the single heading “class noun.” For, in the grammarians’ usage, these five universals are all class nouns; a class noun (1) for them is a word predicated of a thing and of whatever resembles it, corresponding to what the logicians call a “universal.” Thus, the very term that the logicians call “universal,” or the meaning they describe as “universal,” is what the grammarians label a class noun.

Accordingly, when it is said, “The things that exist share the designation ‘existence,’” it is like saying, “Substances share the designation ‘substance,’” “Bodies share the designation ‘body,’” “Animals share the designation ‘animal,’” “Human beings share the designation ‘human,’” and even, “Arabs share the designation ‘Arab.’” Examples of this kind are too numerous to count.