Simplicius: I mean the centre of the universe, of the whole world, of the starry sphere.
Salviatus: No one has ever proved that the universe is finite and figurative; but granting that it is finite and spherical, and has therefore a centre, we have still to give reasons why we should believe that the earth is at its centre.
Simplicius: Aristotle has proved in a hundred ways that the universe is finite and spherical.
Salviatus: Aristotle's proof that the universe was finite and spherical was derived essentially from the consideration that it moved; and seeing that centre and figure were inferred by Aristotle from its mobility, it will be reasonable if we endeavour to find from the circular motions of mundane bodies the centre's proper place. Aristotle himself came to the conclusion that all the celestial spheres revolve round the earth, which is placed at the centre of the universe. But tell me, Simplicius, supposing Aristotle found that one of the two propositions must be false, and that either the celestial spheres do not revolve or that the earth is not the centre round which they revolve, which proposition would he prefer to give up?
Simplicius: I believe that the Peripatetics——
Salviatus: I do not ask the Peripatetics, I ask Aristotle. As for the Peripatetics, they, as humble vassals of Aristotle, would deny all the experiments and all the observations in the world; nay, would also refuse to see them, and would say that the universe is as Aristotle writeth, and not as Nature will have it; for, deprived of the shield of his authority, with what do you think they would appear in the field? Tell me, therefore, what Aristotle himself would do.
Simplicius: To tell you the truth, I do not know how to decide which is the lesser inconvenience.
Salviatus: Seeing you do not know, let us examine which would be the more rational choice, and let us assume that Aristotle would have chosen so. Granting with Aristotle that the universe has a spherical figure and moveth circularly round a centre, it is reasonable to believe that the starry orbs move round the centre of the universe or round some separate centre?
Simplicius: I would say that it were much more reasonable to believe that they move with the universe round the centre of the universe.