Print ISBN 9780199246533, 2001 pp. -
hearing the clock chime as you're helping the student understand the theorem you're teaching her. The intended absurdity is associated with a case in which the mover is being moved with the very same, most specific species of motion as that with which the mover is doing its moving—a case in which, for example, you are being taught the very same theorem you're teaching in the very same way you're teaching it at the very same time you're teaching it (not even a little earlier). For in that case you would (as teacher) have and (as learner) not have the very same thing in the very same respect at the very same time, which is absurd.
Well, all right, that can't happen. But even if we grant, for the sake of the argument in stage lb, that there are only three genera of motion, we're bound to say that there must be infinitely many most specific species of those three genera. Just think, for instance, of all the propositions that might be taught. It is simply false—or, at any rate, unbelievable—that 'there are finitely many genera and species of motion' (lines 14-15) in the sense of 'species of motion' required for stage lb. And so it's illegitimate to try running the argument by merely ringing the conveniently few changes on the three genera, as in lines 11-14 and 19-21.
But suppose someone were to push the teaching example harder (trading on what must be admitted to be favourable features peculiar to it) and claim that if you are teaching theorem 45 now, you must once have been taught that very theorem. Thus, in moving your student in accordance with the species of motion that is teaching-theorem-45 you are 'moved in accordance with the same species, albeit not directly, but indirectly' (lines 23-4). Clearly there is a sense in which your once having been moved with that most specific species of motion is a moving of you that would be most explanatory of your being able now to move your student with that same species of motion. But in view of the fact that the simultaneity condition is not satisfied in this case, it doesn't violate the principle of non-contradiction, as the first one did. So, what's supposed to be absurd about the mover's being moved not at the very same time—one legitimate interpretation of being moved /'ndirectly—by the very same most specific species of motion in the very same respect? We are not told. And so the general point cannot be made even on the basis of what seems to be its most advantageous sort of example.
Perhaps there is an even simpler objection to stage lb. For even end p.71
if there were something intolerable about recycling species of motion all the way back to the species instantiated in the terminating motion (as Aquinas claims there is, in lines 16-24), why couldn't there be cases in which only the other two species are recycled, thereby avoiding the outcome he thinks is absurd? Let Z be the last moved mover in a beginningless series of moved movers. And suppose that Z is moving whatever it moves locally and that it is the only local mover in the series, and that Z is moved by Y, which is moving Z by alteration and is moved by X, which is moving Y by increase and is moved by W, which is moving X by alteration and is moved by V,
which is moving W by increase . . . , and so on, ad infinitum.
40 The version of this argument in the parallel passage (In Phys. VIII: L9.1046-7) is fuller, but no better.
Of course, there's much more that could be said about G2's stage lb, and some of what could be said might be favourable; but there's no point in going further with it now. As it stands, it can't be saved. So stage I's a priori argument—not the sort of argument Aquinas has led us to expect in this chapter—does not succeed in reducing 'Every mover is moved by something else'to an absurdity. Consequently, G2 has not established the existence of 'some first mover that is not moved by anything extrinsic to it'. I think Aquinas would have done better to leave this argument where he found it, in
41 There is a second Aristotelian argument in VIII 5 to this same effect (beginning at 257a4), and Aquinas develops it in his commentary (VIII: L9.1048), though not as part of G2 in SCG 1.13. It strikes me as illuminating some features of what I'm calling stage lb, but not as a better argument to the same conclusion.
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