 Interestingly, particularly in comparison with the Western tradition, the Mohists do not regard the fallibility of perceptual or cognitive processes as grounds for doubt. In their view, the sources of doubt lie not in the nature of the cognitive subject, but in contingent features of particular circumstances—that they are potentially confusing, atypical, causally overdetermined, transient, or simply provide inadequate evidence. With the exception of causal overdetermination, in most cases doubt can be resolved by further investigation. Nor is reality considered inherently unknowable, because of incessant phenomenal change or because appearances mislead us as to how things actually are. Accordingly, ancient Chinese skepticism—as expressed in the Zhuangzi, for example—is not concerned with the unreliability of sense perception or a gap between appearance and reality, but with the problem of grounding the norms by which we draw distinctions between things. 