Coming after Muʾayyad al-Dīn al-ʿUrḍī (1200–1266) and Naṣīr al-Dīn al-Ṭūsī (1201–1274), Quṭb al-Dīn al-Shīrāzī (1236–1311), a leading figure of the so-called Marāgha school in astronomy, presents his predecessors’ non-Ptolemaic models and criticizes them in his three hayʾa books. Since his own new models in Nihāyat al-idrāk (written in Arabic in 1281) and Ikhtiyārāt muẓaffarī (written in Persian in 1282) are not without difficulties, in his latest book on hayʾa, al-Tuḥfa al-shāhiyya (written in Arabic in 1285) he puts forward his modified models inspired from Ṭūsī’s and ʿUrḍī’s models and produces a series of new models for Mercury and the oscillation of the spheres. Nevertheless, in spite of all his attempts, the tradition of non-Ptolemaic modeling after him never converged to a series of standard models.

The twelfth century philosopher-theologian Fakhr al-Dīn al-Rāzī is well known for his critique of Avicennan metaphysics. In this paper, I examine his critique of Avicenna's physics, and in particular his rejection of the Avicennan and Aristotelian theory of place as the inner boundary of a containing body. Instead, Fakhr al-Dīn defends a definition of place as self-subsisting extension, an idea explicitly rejected by Aristotle and Avicenna after him. Especially in his late work, the Maṭālib, Fakhr al-Dīn explores a number of important philosophical issues with reference to this theory of place, including the principle that two indiscernible things (in this case two overlapping extensions) must be identical and the idea that motion and rest are always relative.

Avicenna's analysis of the definition of substance and accident repeatedly emphasizes two points: one and the same essence cannot be substance in one instance and accident in another; whether x is extrinsic or intrinsic for an underlying subject, y does not tell us anything as to whether x is substance or not. Both points are development in an argument against certain unnamed people who claimed the opposite. In this article I will show that Avicenna's opponents are to be identified with the mainstream Baghdad Peripatetic School (Ibn Suwār, Ibn al-Ṭayyib) which based itself on the Late Antique rule that “parts of substances are substances”. As for Avicenna's own position, it was developed on the basis of the heterodox position of Yaḥyā b. ʿAdī, who anticipated Avicenna's first point. This is a further piece of evidence for something that has only recently begun to be appreciated: the influence of Ibn ʿAdī on Avicenna.

This study investigates the problem of the natural universal (kullī ṭabīʿī) in the works of Mullā Ṣadrā (d. 1640). The problem of universals made its way into Arabic/Islamic philosophy via its Greek sources, and was transformed into the problem of natural universals by Avicenna. Weighing in on this problem, Ṣadrā reinterprets the nature of natural universals against the backdrop of his doctrine of “the primacy of being.” As he argues, a natural universal or quiddity qua quiddity is an “accidental being” that requires wujūd for its existentiation. Thus, Ṣadrā re-envisions the status of natural universals by stripping them of their disputed status as independently existing entities.