Osiander and Anti-realism

This is another post from the frontlines of the class I'm teaching on Early modern philosophy and the scientific revolution. For those who haven't ever looked at Copernicus's On the Revolutions of the Heavenly Spheres, the book's first preface is written by a man named Andreas Osiander (though this preface was left unsigned in the original work).

In this preface, Osiander advocates for (what today would be called) an anti-realist conception of astronomy: the aim of astronomy is not to arrive at "true or even probable hypotheses," but rather to construct a mathematical model that will generate accurate predictions of the observed apparent locations of the celestial bodies.*

Osiander has come in for a lot of criticism, both from his contemporaries (like Rheticus, who entrusted the publication of Copernicus's book to him) as well as current commentators. However, I think the justifications Osiander offers for his view that we should not take astronomical models as literally true are not crazy. First, he notes that, if Ptolemy's model is correct, Venus's apparent size in the sky should change a great deal more than it actually does. That is obviously an empirical argument that Ptolemaic models do not reveal the true structure of the cosmos -- even though these models do make accurate predications about the location of Venus in the nighttime sky. Second, Osiander claims that there are genuine incompatible theories that both account equally well for the phenomena: he asserts that the Sun's observed motion can be modelled using an eccentric circle as basis or using an epicycle. (Unfortunately, I don't know anything about the details of this example.) If this is a genuine example of inconsistent but observationally equivalent theories, then Osiander has as good an argument against interpreting astronomical theories as literally (approximately) true as any argument given by an anti-realist motivated by underdetermination arguments.

Finally, note that these reasons for anti-realism are specific to astronomy. Thus we should not take Osiander to be advocating a general anti-realism towards all of science. To borrow the terminology of Magnus and Callander's recent "Realist Ennui" paper in Philosophy of Science, Osiander is not offering a "wholesale" argument for anti-realism, but a "retail" one, i.e., one specific to our pretensions to knowledge of the true physical structure of the universe.

________
* Tagging Osiander with various forms of anti-realism has been contested; see Barker and Goldstein's 1998 "Realism and Instrumentalism in Sixteenth Century Astronomy: A Reappraisal," in Perspectives on Science. They do agree, however, that Osiander considers knowledge of the true physical characteristics of the cosmos to be forever beyond human reach -- which strikes me as something a modern anti-realist might say. They also make the last point in the above post -- Osiander's skepticism is restricted to astronomy.