 Kant’s argument might be that the matter of experience (its sensory content) depends upon how our sensibility is affected by mind-independent objects, things in themselves, while the form of experience is determined by our minds alone. Consequently, experience itself requires the existence of objects “outside” (in the transcendental sense) the mind. But this would show, at most, that Kant is not a strong phenomenalist. It does not undercut the interpretation of him as a qualified phenomenalist. Nor does it succeed in clearly differentiating him from Berkeley. (See the supplementary article:  Kant’s Attempts to Distance Himself from Berkeley.)  This, of course, does not settle the issue; it may be that Kantian appearances are quite different than bodies, as Berkeley, or even the qualified phenomenalist, conceive them (for important discussions of transcendental idealism in the Prolegomena see Ak. 4:283–4, 286, 289–294, 314–315, 320).