 At one point in Walden, Thoreau quips that he usually does not count himself among the “true idealists” who are inclined to reject “the evidence of [their] senses” (Walden, XIV). On the other hand, he has nothing but scorn for the sort of materialism that fails to penetrate the inner mystery of things, discovering “nothing but surface” in its mechanistic observations (Journal, 3/7/59). Instead, he argues that we must approach the world as “nature looking into nature,” aware of the relation between the form of our own perception and what we are able to perceive (Correspondence, 7/21/41). There are reasons for classifying Thoreau as both a naturalist and a romantic, although both of these categories are perhaps too broad to be very helpful. His conception of nature is informed by a syncretic appropriation of Greek, Roman, Indian, and other sources, and the result is an eclectic vision that is uniquely his own. For this reason it is difficult to situate Thoreau within the history of modern philosophy, but one plausible way of doing so would be to describe him as articulating a version of transcendental idealism. If Thoreau is indeed “the American heir to Kant’s critical philosophy,” as he has been called (Oelschlaeger 1991, 136), it is because his investigation of “the relation between the subject of knowledge and its object” builds upon a Kantian insight that Emerson, who viewed the senses as illusory, arguably did not grasp (see Cavell 1992, 94–95). Yet in order to understand why this might be an accurate categorization, we must proceed from Thoreau’s metaphysics to his epistemology.