A medieval Arabic analysis of motion at an instant : the Avicennan sources to the forma ﬂuens/ﬂuxus formae debate
British Journal for the History of Science 39(2): 1–17, June (2006) British Society for the History of Science
The forma fluens/fluxus formae debate concerns the question as to whether motion is something distinct from the body in motion, the flow of a distinct form identified with motion (fluxus formae), or nothing more than the successive states of the body in motion, the flow of some form found in one of Aristotle’s ten categories (forma fluens). Although Albertus Magnus introduced this debate to the Latin West he drew his inspiration from Avicenna. This study argues that Albertus
misclassified Avicenna’s position, since Albertus could not conceptualize motion at an instant, whereas it is claimed here this was the very position Avicenna adopted. The paper includes an overview of Albertus’s discussion and a brief survey of the Avicennan sources upon which Albertus drew. The heart of the paper treats Avicenna’s analysis of motion at an instant. Avicenna’s general argument was that since spatial points have no extremities, nothing in principle prevents a moving object from being at a spatial point for more than an instant, understood as a limit. It is then argued that Avicenna had the philosophical machinery to make sense of a limit, albeit not in mathematical terms, but in terms of an Aristotelian potential infinite.