 Aristotle had in his physical writings addressed and critiqued atomism (e.g., Aristotle, Physics, 6.1 and On Generation and Corruption, 1.2). In the time between Aristotle and Avicenna, however, there were a number of developments in atomic theory both by Epicurus, one generation after Aristotle, and by Muslim theologians, that is, proponents of Kalām, most of whom were atomists (Dhanani 1994, 2015). As a result, Avicenna’s critique of atomism needed to address new innovations and challenges. One such innovation, which can be traced back to the Greek world, is a distinction between physical divisibility and conceptual divisibility. Thus, for example, the atoms of  Democritus  (d. 370 BCE) have as one of their properties shapes. If atoms have a shape and to have a shape is to have definite limits, then one might reason that Democritean atoms have distinct limits into which they can at least be conceptually divided, even if not physically divided. Aristotle in fact exploited this point in his critique of Democritus. In contrast, the minimal parts of  Epicurus  (d. 270 BCE) had no shape, and so were not subject to the same criticism. Indeed, Epicurean minimal parts are purportedly not merely physically indivisible but also conceptually indivisible. To provide a rough and ready image of an Epicurean minimal part, one might think of the surface thickness of a plank, and the plank itself as the aggregation of such surfaces. For example, then, when the surfaces of two planks are brought together tightly, intuitively one may think that the two surfaces remain two distinct physical things; the bottom of the top plank, for instance, is distinct from the top of the bottom plank. When some enormous number of these surfaces is aggregated, a plank with a definite thickness, one might imagine, results. So how thick are these surfaces? One cannot fathom, but again being so thin that dividing it further is inconceivable is the very point of Epicurus’ minimal parts. Whatever the chain of transmission, it was something much like Epicurus’ minimal parts that Muslim atomists identified with their atoms, or more precisely, indivisible parts (sing. al-juzʾ alladhī lā yatajazzaʾu)—a spatial magnitude that was not merely physically indivisible but also conceptually indivisible. 