In his account of the methods of Voltaire’s Zadig, who astounded his listeners by his ability to visualize an animal from the tracks it had left behind, Thomas Huxley likened Zadig’s conclusions to ‘retrospective prophecies’ (Huxley, 1882: 132). Anticipating the objection that this might seem a contradiction in terms, Huxley argued that prophetic reasoning rests on the same procedures whether they be applied retrospectively or prospectively. For ‘the essence of the prophetic operation’, as he put it, ‘does not lie in its backward or forward relation to the course of time, but in the fact that it is the apprehension of that which lies out of the sphere of immediate knowledge; the seeing of that which to the natural sense of the seer is invisible’ (132). Between the two cases, then, the process remains the same; it is only the relation to time that is altered.