 Perhaps drawing on an argument of Aristotle’s (Sens. 7, 449a20–31]), Diodorus apparently used the idea that there is a smallest size at which an object at a given distance is visible as the basis for an argument that there are indivisible magnitudes. His argument begins from the idea that there is a difference in size between the smallest size at which a given object is visible—presumably from a given distance—and the largest size at which it is invisible. Unless we concede that, at some magnitude, a body is both invisible and visible (or neither), there cannot be any other magnitude intermediate between these two magnitudes. Magnitudes must increase by discrete units.