The principle of simplicity for Quṭb al-Dīn Shīrāzī

This paper seeks to show how Quṭb al-Dīn Shīrāzī, a prominent astronomer of the Islamic age of science, employed the principle of simplicity in choosing among rival planetary models. Following some previous studies, we distinguish syntactic and ontological accounts of simplicity. Shīrāzī explicitly refers to these methodological principles and utilizes them to reduce the number of orbs in the planetary models. We provide cases where Shīrāzī applies the former account of simplicity, and others where he uses the latter. In some complicated cases, however, he appeals to a third kind of simplicity in favor of conceptual consistency. We argue that retaining the uniform motion of orbs plays a critical role in his favoring a particular account of simplicity.