 An added benefit of Avicenna’s introduction of this new species of motion is that it provides him an easy answer to what has been called “la grande question” of ancient celestial physics (Hasnawi 1984). As a bit of background to the problem, Aristotle defined a thing’s “where,” or place, with the outermost containing limit of the surrounding body (Aristotle, Physics, 4.4, 212a20) and Avicenna followed Aristotle faithfully on this point (Avicenna, [Ph], 2.9 [1–3]; Lammer 2018, §§5.1–2). Thus, only a body that has a body outside of it and containing it can have a place. Consequently the outermost celestial sphere “beyond” which there is absolutely nothing, by definition cannot have a place. The problem, then, is this: We observe the outermost celestial sphere apparently making a complete rotation once approximately every twenty-four hours, but what specific sort of motion is the outermost celestial sphere undergoing? Aristotle and the earlier tradition had identified only three species of motion: motion with respect to quantity, quality and place. Clearly the motion of the heavens is neither a change in quantity nor a change in quality, but it is also not a change of place, since, as we have seen, the outermost celestial sphere has no place. Avicenna’s introduction of positional motion provides an obvious solution: the outermost celestial sphere is moving with respect to the category of position. Moreover, Avicenna’s solution is not ad hoc, since he has integrated his account of positional motion into his general analysis of motion and motion’s relation to the categories. 