In the Critique of Pure Reason, under "System of the Principles of the Pure Understanding, Section II Of the Highest Principle of all Synthetical Judgments" Kant writes, 2nd last paragraph:
"As therefore experience, being an emirical synthesis, is in its possibility the only kind of knowledge that imparts reality to every other synthesis, this other synthesis, as knowledge a priori, possesses truth (agreement with its object) on this condition only that it contains nothing beyond what is necessary for this synthetical unity of experience in general...
"Thus synthetical judgments a priori are possible, if we refer the formal conditions of intuition a priori, the synthesis of imagination, and the necessary unity of it in a transcendental apperception to a possible knowledge in general, given in experience, and if we say that the conditions of the possibility of experience in general are at the same time conditions of the possibility of the objects of experience themselves, and thus possess objective validity in a synthetical judgment a priori."
While I'm able to decipher this, the translation is F. Max Mueller's, and I think it suffers a little, especially the 2nd part quoted. What are your thoughts as to the term "transcendental appeception" ... as a rather ambiguous one? Kant is connecting this to a synthesis of imagination ... an understanding derived entirely by means of pure reason, and the objective validity of which is given by our connecting this understanding to the world of experience. Hence, I interpret this to mean that this is a critical demand on Kant's part with regard to metaphysical knowledge/understanding, ie.: a science of metaphysics applicable to reality. This interpretation flies in the face of those who would interpret Kant's Critique as an attack on metaphysics, and hence, pure speculative reason. But I would say, only an attack on those systems of metaphysic that fail to make sense of the world of experience. Any clarification/comments?