 In the Perfect City Fârâbî says that the First causes existence, immediately and without cooperation with an instrument or matter, only to a single thing, the Second; in the Political Regime, apparently, the First causes existence immediately to several things, the Seconds. But in both treatises, when he introduces his discussion of the First as the cause of existence to other things, he does not start by singling out a Second or Seconds. Rather, he starts by saying that “the substance of [the First] is a substance from which every existence emanates, whatever this existence may be like, whether it is perfect or deficient”; (Walzer 1985,  94),[59]  but he then immediately adds that “when all the beings arise from it, they are ordered in their ranks, and each being receives from it the portion of existence which is due to it and the rank which is due to it”  (ibid.).[60]  But then there is a problem why the First’s single simple existence, assuming that it causes the existence of something else, should cause a plurality of beings receiving greater or lesser “portions” of existence from it. Fârâbî’s answer to this problem seems to be less developed in the Political Regime than in the Perfect City. In the Political Regime, he says that the Seconds (the intelligences that move the heavenly bodies), and apparently also the “active intelligence” that governs the sublunar world, “have all received existence from the First” (Butterworth 2015, 46, #34, translation modified); other things depend on the Seconds or the active intelligence for their existence, and for this reason receive lesser portions of existence. Fârâbî says here that the Seconds, like the First, are such that their specific existence is sufficient for the existence of something else to emanate from them (ibid.): each Second produces a heavenly sphere composed of body and soul (it produces not merely the motion but the existence of the sphere), and sublunar substances depend for their existence both on the heavenly spheres and on the active  intelligence.[61]  The Political Regime says that the Seconds have different ranks (Butterworth 2015, 46, #34) but it does not say anything to explain why there should be many of them or why they should differ in rank. In particular, it does not say that lower Seconds depend on higher Seconds for their existence: each Second is described only as producing a heavenly sphere, not as producing another Second, and as far as we can tell each Second is produced immediately by the First without cooperation with any other cause. However, in the Perfect City, Fârâbî says that the First, immediately and by itself alone, produces only a single Second (Walzer 1985, 100), and that all other beings are produced by the First in conjunction with instruments or material substrata, where these must be either the Second or things which are produced by the First in conjunction with the Second. This allows Fârâbî to explain why there should be a plurality of separate immaterial substances, and why they should differ in rank: the Second which is immediately produced by the First has a greater “portion of existence” than the Third which depends essentially on the Second, and so on, and all of these separate intelligences (the movers of the heavenly spheres and then the active intelligence that governs the sublunar world) have greater portions of existence than sublunar substances which essentially depend on the heavenly spheres and on the active intelligence. Here Fârâbi is following out the program of Book of Letters I,92, discussed above, of finding a single first substance (here the Second, i.e., the mover of the outermost heavenly sphere) on which all other substances are essentially dependent, and then tracing it back in turn to a single simple First: the causal definition of any other substance, if made fully explicit, would have to refer to the motion of the outermost sphere and to the Second as its cause, and thus ultimately to the First. But Fârâbî has the problem of explaining how a single Second can be responsible for causing all this multiplicity of essentially differing beings. The Perfect City, like the Political Regime, stresses that the Seconds (or Second, Third, and so on), like the First, are each an intelligence which is essentially actually cognizing and is itself the object it cognizes, and whose specific existence is sufficient for the existence of something else to emanate from it; both treatises also stress that these intelligences are also inferior to the First, notably in that they do not have their full perfection purely in themselves, but only through a relation to the First, namely through intellectually cognizing the First. But if each of these intelligences, like the First, immediately produces only a single being like itself, they will not be able to explain the multiplicity and complexity of the beings that arise indirectly from the First. In the Political Regime apparently each of the Seconds produces just a single being, namely the heavenly sphere it governs (although this sphere has some complexity as a compound of body and soul, and although the active intelligence that governs the sublunar world has more complex effects), but in the Perfect City each of these intelligences has to produce two beings, namely the heavenly sphere it governs and the next  intelligence.[62]  Thus