 Outlines of metaphysics, of various lengths, can be found in Avicenna’s treatises on the classifications of the sciences, as well as in the surveys of the different branches of philosophy interspersed in many of his other works. These epistemological sketches are substantiated in his summae, a literary genre of which he can be considered the inventor. In all these “encyclopedias” of philosophy—addressed to different audiences and displaying various formats, methodologies and styles—metaphysics constitutes, together with logic and natural philosophy, a permanent and pivotal part of philosophy. In those written in Arabic, after the propaedeutic treatment of logic, the sequence of theoretical disciplines is given—along traditional lines—as natural philosophy, mathematics, and metaphysics, or simply as natural philosophy and metaphysics, with mathematics frequently omitted. By contrast, in the Persian summa, Philosophy for ʿAlāʾ al-Dawla (Dānišnāmah-yi ʿAlāʾī), and possibly also in the incompletely extant Eastern Philosophy (Al-Ḥikma al-mašriqiyya), the order is reversed and, as Avicenna himself avows, much more original: metaphysics constitutes the beginning, rather than the end, of theoretical philosophy. These two opposite arrangements are in fact compatible and underscore complementary aspects of the primacy of metaphysics within theoretical philosophy: metaphysics is last in the order of learning as the pinnacle of philosophical instruction, while it is first in the order of reality on account of the supreme rank of the things it deals with.