  Conceptually, we might think of the process as the mind rearranging the ontological structure of the object. As a substantial artifact, what-it-is, the sand box has certain properties essentially. The figure drawn may be incidental to what-it-is, i.e., an accident. In treating the object as the figure drawn, being made of sand is incidental to it. Hence, ‘things by removal’ may be one way of explaining perceptible magnitudes qua lengths. This is the concept which does most of the work for Aristotle.