  Now one might endeavour to support Russell’s contrary view by arguing that non-zero speed is both necessary and sufficient for motion. But both sides of this equivalence might be disputed. On the necessity of non-zero speed for motion, a challenge might be mounted that zero speed but non-zero acceleration is motion. On the question of the sufficiency of non-zero speed for motion, Priest in the second edition of In Contradiction (2006) says that he does not deny this. But this opens him up a possible objection, namely that if non-zero (speed or acceleration) is necessary and sufficient for motion, then the extra element of inconsistency would seem to be explanatorily otiose, since there is no need to add the extra element of inconsistency in order to constitute motion. Such an objection does not refute his view, but it would seem to make it unsimple. Moreover, one might still adopt an inconsistent view coupled with the denial of sufficiency, which avoids this objection.