 Idealism and phenomenalism are views that hold that ordinary objects (tables, clouds, rocks, etc.) are really collections of or constructs out of actual and/or possible mental states, especially perceptual experiences. (I won’t try to distinguish phenomenalism from idealism but will use “idealism” to include both.) There are several varieties of idealism and several motivations for holding the view. But one motivation is that it promises to solve the skeptical problem of the external world. Berkeley (1710) held that idealism was a cure for skepticism. Transcendental idealism (Kant 1781) aims to split the difference with the skeptic by distinguishing the phenomenal objects of perception—which are collections of appearances and about which we can know something—from the noumenal objects—which are things in themselves and not mere appearances, and about which skepticism is true.