 In order to disprove the possibility of external objects, Vasubandhu delves into the atomic theory of the Kashimiri Vaibhāṣikas as well as that of the (“orthodox”/Hindu)  Vaiśeṣikas.[39]  The purpose here is to undermine every possible theory that might account for perception as caused by non-mental entities. Vasubandhu’s argument at this stage is entirely based in mereology—the study of the relations between parts and wholes. He argues first that atomism—the view that things are ultimately made up of parts that are themselves partless—cannot work. Then, he argues that any reasonable explanation of objects of perception must be atomic, by arguing that the alternative—an extended, partless whole—is incoherent. Vasubandhu takes it that together, these conclusions prove that external objects must be unreal appearances.