 Cardinal Bellarmine was willing to countenance scientific truth if it could be proven or demonstrated (McMullin 1998). But Bellarmine held that the planetary theories of Ptolemy and Copernicus (and presumably Tycho Brahe) are only mathematical hypotheses; since they are just calculating devices, they are not susceptible to physical proof. This is a sort of instrumentalist, anti-realist position (Machamer 1976; Duhem 1985). There are any number of ways to argue for some sort of instrumentalism. Duhem (1985) himself argued that science is not metaphysics, and so only deals with useful conjectures that enable us to systematize phenomena. Subtler versions of this position, without an Aquinian metaphysical bias, have been argued subsequently and more fully by Van Fraassen (1980) and others. Less sweepingly, it can reasonably be argued that both Ptolemy and Copernicus’s theories were primarily mathematical, and that Galileo was defending not Copernicus’s theory per se, but the physical realization of it. In fact, it might be better to say the Copernican theory that Galileo was constructing was a physical realization of a simplified version of Copernicus’s theory, which dispensed with many of the technical details (eccentrics, epicycles, Tusi couples and the like). Galileo would be led to such a view by his concern with matter theory, which minimized the kinds of motion ascribed uniformly to all bodies. Of course, when put this way, we are faced with the question of what constitutes identity conditions for a theory. Still, there is clearly a way in which Galileo’s Copernicanism is not Copernicus’s.