The author begins with an outline of Bernard William's moral philosophy, within which he locates William's notorious doctrine that reflection can destroy ethical knowledge. He then gives a partial defence of this doctrine, exploiting an analogy between ethical judgements and tensed judgements. The basic idea is that what the passage of time does for the latter, reflection can do for the former: namely, prevent the re-adoption of an abandoned point of view (an ethical point of view in the one case, a temporal point of view in the other). In the final section the author says a little about how reflection might do this.