In his seminal article on “The Dynamics of the Leaning Tower Experiment” published in 1951, Ernest Moody discussed Galileo’s evolving views of motion in a void and its origins in the medieval Latin sources. The medieval Latin discussion of this problem, which as Moody notes derives from Text 71 of Aristotle’s Physics, was influenced by Averroes Large Commentary on the Physics in which the dissenting view of Avempace or Ibn Bājja (d. 1139) is found, namely that motion of a void cannot be instantaneous and is therefore possible. Ibn Bājja’s view is not unique in Islamic natural philosophy. It is found among the pre-Avicennan mutakallimūn, where it is formulated within the framework of atomist physics in which the fastest atomistic motion of one spatial unit in one temporal unit. The post-Avicennan discussion of Fakhr al-dīn al-Rāzī (d. 1209) is not formulated within atomistic physics, but
rather as a critique of Aristotelian dynamics, just as it is in Ibn Bājja. This begs the question of whether this critique of Aristotelian dynamics is somehow related to the earlier kalām discussion, or whether the formulations of Ibn Bājja and Fakhr al-dīn al-Rāzī are drawing from an older tradition of the critique of Aristotelian dynamics. In my discussion, I will focus on the pre-Avicennan kalām discussion of motion in a void, then contrast it with the formulations of Ibn Bājja and Fakhr al-dīn al-Rāzī, and finally speculate on the relationships of these formulations with each other and with earlier discussions on this question.