This chapter returns to the compare-and-contrast approach of Part I, focusing this time on van Fraassen's constructive empiricism. The constructive empiricist holds that no evidence can support the claim that unobservable entities exist, which seems to deny the force of the accepted scientific evidence for the existence of atoms. In a move familiar from Kant, Carnap, and Putnam, van Fraassen agrees that the Second Philosopher's evidence is valid for her purposes, but posits another level of inquiry — philosophical or epistemological inquiry — where the existence of atoms can never be confirmed. As before, the Second Philosopher sees this other inquiry as unmotivated and its methods unclear, but this doesn't ally her with van Fraassen's opponents, the scientific realists, who join him in thinking the ordinary evidence needs some kind of supplementation. The chapter closes with an examination of Worrall's anti-naturalism.
Keywords: atoms, Carnap, constructive empiricism, Kant, Putnam, scientific realism, unobservables, van Fraassen, Worrall