 The demonstration was certainly not about the collection of jagged black surfaces that we can see here. Rather, the demonstration concerned something we did not see with our bodily eyes, but what we had in mind all along, understanding it to be a triangle, with perfectly straight edges, touching a perfect circle in three unextended points, which are all perfectly equidistant from the center of the circle. The figure we could see was only a convenient “reminder” of what we are supposed to have in mind when we want to prove that a certain property, namely, that it is a right triangle, has to belong to the object in our mind in virtue of what it is, namely, a triangle inscribed in a semicircle. Obviously, the conclusion applies perfectly only to the perfect triangle we had in mind, whereas it holds for the visible figure only insofar as, and to the extent that, this figure resembles the object we had in mind. But this figure fails to have this property precisely insofar as, and to the extent that, it falls short of the object in our mind.