In relation to a prior posted question (which I didn't feel recieved adiquate response), how does Kant claim that observations of objective reality prove something beyond the phenomena, namely noumena? I don't see a necessary link between them, to state there must be a reality beyond perception, within the prolegomena (unless pure reason would be a better source).
According to Kant, next to nothing can be know about the noumena except for its existence, and that is primarily a question of definition; i.e. if there is no such thing as noumena, it doesn't make sense to speak of phenomena:
"At the same time, it must be carefully borne in mind that, while we surrender the power of cognizing, we still reserve the power of thinking objects, as things in themselves. For, otherwise, we should require to affirm the existence of an appearance, without something that appears—which would be absurd" (Critique of Pure Reason, Preface to the Second Edition, Bxxvi)
I find it questionable whether Berkeley could even be considered as denying noumena, because he didn't deny appearances. Something had to be the cause of them, and that cause would then be considered noumena. Therefore, as Kant says, there's no way to deny noumena except to claim that there is no such thing as appearances. I don't believe that Kant addressed that possibility, but I doubt that he would have considered it a tenable position.