Astronomical Images : Instant of time in alteration

Aristotle

Astronomical Images

This work comprises Aristotle's Physics and Thomas Aquinas's commentary edited by the Augustinian, Timoteo Maffei of Verona (d. 1470). Aristotle discussed the nature of motion in the latter books of Physics, often referring to figures to elucidate his points. These figures were not always illustrated, and there was no traditional stock of figures like the wind diagrams or concentric circles associated with the Aristotelian analysis of motion. This edition makes an effort to supply such figures. In Physics, book 8, chapter 8, Aristotle makes the point that the instant which divides past and future time performs a double function: marking the end of the past and the beginning of the future. But the point that divides states that counteract each other ' so that the object is always in either the one or the other ' does not have a dual function. This is shown with the example of white turning into black. In the figure, time is represented as a bar, with the periods A and B divided by a momentary instant, C. Circle D, beneath point A, represents a mobile that is white during the whole of A; it is also shown under B with a thick black circle to indicate that it is not-white during the whole of B. So then at the instant C, D will be both white and not-white; for if it is really white during the whole of A, it must be true that it is white at any instant of A, and in B it is not-white, and C is in both A and B. So one should not allow that it is white at every point of A, but only at every point of A except the terminating instant C. This instant already belongs to B and if D occupied the whole time A in the process of becoming non-white or of ceasing to be white, either process was complete at the instant C. Unless it is conceded that a white thing can be truly described as not-white at that instant for the first time, it is necessary to say that a thing does not exist at the instant when it has ceased to be, or else that it must be both white and not-white, or more generally both existent and non-existent at the same instant. (Aristotle, Physics VIII.8.263b9-26, trans. Wicksteed and Cornford.)