 The introduction of positional motion, however, brings with it a new challenge. According to Avicenna, motion always involves a terminus a quo, that is, a “from which,” (mā minhu) and a terminus ad quem, that is, a “to which” (mā ilayhi) (Avicenna, [Ph], 2.1 [12 &amp; 20–22]). His reason for insisting on this point is that motion, as noted, is the actuality of potential as potential, where the initial state of potentiality corresponds with the terminus a quo and the final state of actuality corresponds with the terminus ad quem. The difficulty is that there need be no starting and ending point for rotation, particularly if, as Avicenna believes, the rotation of the heavens has neither beginning nor end. Avicenna’s response to this challenge involves a sophisticated analysis of the various ways of understanding actuality and potentiality (including an appeal to the first and second actuality already noted but also introducing a notion of remote and proximate potentiality). Without going into the details, the general intuition of his response is simple enough (for a detailed account see McGinnis 2006b). As a matter of supposition, one can posit within the continuous rotational motion of, say, a celestial sphere some point, for example, the sun’s position when it is directly overhead. In positing that point, one by supposition indicates an initial terminus a quo of the motion, but that same point also indicates a terminus ad quem for that motion (although the two termini are in a sense also different since there is a difference in time between the two instances of being at that point). Thus, for example in our case, a complete sidereal day is actualized when the sun moves from a position directly overhead—the terminus a quo—and then returns to that position—the terminus ad quem. Of course, nothing about this analysis requires that the rotation must cease once this sort of terminus ad quem, which is a proximate potency, has been actualized. Indeed it can be posited as a new terminus a quo for a new rotation. In short, rotational motion still has a terminus a quo and a terminus ad quem corresponding with a potentiality and actuality, even though such motion need have no absolute beginning or ending point. 