 It is not inconceivable that Kant knew of Collier’s work through Eschenbach’s translation, although there is no direct evidence for that. It is more likely that Collier’s argument that the difference between what we ordinarily take to be a veridical perception and a mere imagination or hallucination is merely a matter of vividness, and that the latter can become as vivid as the former and thereby undermine any use of vividness as a criterion of externality (1713 [1909: 19–20]), could have been known to Hume and influenced his formulation of the distinction between impressions and ideas in his Treatise of Human Nature (1739–40). So at this point we can turn to Hume.