In the second edition the Analytic of Principles contains as a supplement a “Refutation of Idealism,” which, in opposition to Descartes’s position that the only immediate experience is inner experience, from which we reach outer experience by inference alone, argues that, conversely, it is only through outer experience, which is immediate experience proper, that inner experience—­as the consciousness of my own existence in time—­is possible.  For all time determination presupposes something permanent in perception, and this permanent something cannot be in me (the mere representation of an external thing), but only actually existing things which I perceive without me.  There is, further, a chapter on the “Ground of the Distinction of all Objects in general into Phenomena and Noumena,” with an appendix on the Amphiboly (ambiguity) of the Concepts of Reflection.  The latter shows that the concepts of comparison:  identity and difference, agreement and opposition, the internal and the external, matter and form, acquire entirely different meanings when they relate to phenomena and to things in themselves (in other words, to things in their relation to the sensibility, and in relation to the understanding merely); and further, in a criticism of the philosophy of Leibnitz, reproaches him with having intellectualized phenomena, while Locke is said to have sensationalized the concepts of the understanding.

The chapter on the distinction between phenomena and noumena very much lessens the hopes, aroused, perchance, by the establishment of the non-empirical origin of the categories, for an application of these not confined to any experience.  Although the categories, that is, are in their origin entirely independent of all experience (so much so that they first make experience possible), they are yet confined in their application within the bounds of possible experience.  They “serve only to spell phenomena, that we may be able to read them as experience,” and when applied to things in themselves lose all significance.[1] Similarly the principles which spring from them are “nothing more than principles of possible experience,” and can be referred to phenomena alone, beyond which they are arbitrary combinations without objective reality.  Things in themselves may be thought, but they can never be known; for knowledge, besides the empty thought of an object, implies intuitions which must be subsumed under it or by which the object must be determined.  In themselves the pure concepts relate to all that is thinkable, not merely to that which can be experienced, but the schemata, which assures their applicability in the field of experience, at the same time limit them to this sphere.  The schematism makes the immanent use of the categories, and thus a metaphysics of phenomena, possible, but the transcendent use of them, and consequently the metaphysics of the suprasensible, impossible.  The case would be different if our intuition were intellectual instead of sensuous, or,