Abū al-Aswad al-Duʾalī—when someone recited to him the verse with an unusual wording—remarked, “This is a ḥarf that has not yet reached you.” He was told in reply, “With every ḥarf that has not reached your uncle, do thus.”

For this reason Sībawayh, at the very opening of his Book, sets out the tripartite division into noun, verb, and ḥarf that conveys a meaning yet is neither noun nor verb. He therefore designates the third category as “a ḥarf that conveys a meaning but is neither noun nor verb,” distinguishing it—by the phrase “conveys a meaning”—from the alphabetic letters such as
(alif)
(bāʾ)
(tāʾ),
for these are merely letters of the alphabet.

These utterances become nouns that take inflection once they are combined and bound together, but when they are pronounced in isolation, before composition, they are uttered with a silent ending—just as the names of numbers are pronounced before they are combined and bound, so one says: wāḥid, ithnān, thalāthah. Hence, children are first taught the names of the separate letters—ab, ta, tha—then the compounded sequence, namely abjad, hawwaz, ḥaṭṭī; and they are taught the names of the numbers: one, two, three.

Let us return to the main subject. Division is of two kinds: the division of a whole into its parts—this is the better known and more familiar to minds and languages—and, second, the division of a universal into its particulars, which is so called because universals are “second intelligibles.”

Thus, if someone were to say, “Existence, which in their view is the subject of metaphysics, is either the totality of all that exists or merely a part of it, namely the Necessary or the Possible,” he would be in error. Its subject is the universal existence divided into its species, not a whole divided into its parts; and it is well known that they discuss the essential attributes of universal existence, not the attributes of every individual existent.

The supreme science, according to the logicians, is not a knowledge of something that exists outside the mind. Rather, what lays bare the paltriness of what those people possess and the deficiency of its worth is that this universal existence—