 When Fârâbî says that there are senses of “one” which do not presuppose any plurality and which have no opposite except a bare contradictory—so that there is no sense of “many” opposite to these senses of “one”, although there is a sense of “many” arising from each such sense of “one”—he is interested above all in the sense of “one” as “circumscribed by a quiddity” (first introduced #17). Fârâbî does not assume that the reader will already be familiar with this analysis of a special sense of “one”: he tries to build up to it from other senses of “one” as “circumscribed” in some other way. He starts by talking about a “body circumscribed by a limit that specifies [takhuṣṣu] it” (#16, p.50). “Circumscribed” here has a straightforward literal sense: the body is surrounded on all sides by its limit or boundary. “Specifies” adds that everything inside that limit is the body, and everything outside that limit is not the body. This may connect with “one” as having no partner in some property, since the body is the only thing inside its limit. Fârâbî passes from “one” as a body to a circumscribed by a limit to “one” as a body circumscribed by a place, where a body’s place is, on the Aristotelian analysis, not the limit of the body itself but the limits of the bodies that surround it. Here again, everything that is in the place is the body, and everything that is not in the place is not the body. Thus the limit, or the place, contributes in two ways to making the body one: it makes the parts of the body one with each other, and it makes the body one body distinguished from other bodies, with which it yields the many that “arises from” this sense of one. The unity [waḥda] corresponding to these senses of “one” [wâḥid] is presumably the circumscription [inḥiyâz] by the limit or the place, which is an accident of an underlying  subject.[35]  But Fârâbî denies that if this unity were removed, its subject would thereby become a many: rather, it would fuse with other things into a larger one when the circumscription separating them from each other is removed (#28). Still, these kinds of unity do also unify a divisible subject, as do the unity of what is one as continuous or contiguous or whole. But Fârâbî is building up to a less familiar but more fundamental, non-spatial kind of circumscription which has only the function of distinguishing a one from other ones and not the function of uniting a plurality. Fârâbî talks about the circumscription of a thing by any attribute, which would include limits and places and other accidents such as qualities (some examples at #78), but he concentrates overwhelmingly on the circumscription of a thing by its quiddity. This can happen at different levels of generality—it can be a specific or a generic quiddity (#27). What is circumscribed by a quiddity, unlike what is circumscribed by a limit or a place, need not be a body and need not be divisible, but can be as general as “being” or “thing” (#64). In some cases, if a thing’s circumscription by its quiddity were removed, it would fuse into a one with other ones when it the attributes distinguishing it from these others are removed, as a body circumscribed by a limit or place would fuse into a one with other bodies when its circumscription by its limit or place is removed. If a thing’s circumscription by its specific quiddity were removed, it would still be circumscribed by its generic quiddity, and would fuse into a one with the other things in its genus, but if all circumscription by a quiddity were removed from it, there would no longer be anything left at all (#27). So there is no opposite to this sense of “one” except sheer non-being (#27): there is a sense of “many” arising from this sense of “one”, but it is not opposite to this sense of “one” (#49). The cases of circumscription by a limit or a place might wrongly lead us to think that whenever something is called “one” its unity is an accident attaching to some underlying subject, but in the present case if the unity were removed the quiddity would be destroyed. Fârâbî does seem to distinguish a thing’s unity in this sense from its quiddity when he says that the unity of a species, as circumscribed by its specific quiddity, is the differentia by which it is circumscribed from other species of its genus (#78): but this is still essential to the thing, and we know from the Book of Letters that the differentia can be called the existence of the thing, as here it is called the unity of the thing.