I recently read Berkeley's work entitled "Three Dialogues between Hylas and Philonous" in which he gives an account very similar to that of Kant.
"Appearances, so far as they are thought as objects according to the unity of the categories, are called phenomena.... the word appearance must be recognized as already indicating a relation to something, the immediate representation of which is, indeed, sensible, but which, even apart from the constitution of our sensibility (upon which the form of our intuition is grounded), must be something in itself, that is, an object independent of sensibility. There thus results the concept of a noumenon."
-Immanuel Kant, Critique of Pure Reason
"I say in the first place, that I do not deny the existence of material substance, merely because I have no notion of it, but because the notion of it is inconsistent, or in other words, because it is repugnent that there should be a notion of it. Many things, for aught I know, may exist, whereof neither I nor any other man hath or can have any idea or notion whatsoever. But then those things must be possible, that is, nothing inconsistent must be included in their definition. I say secondly, that although we believe things to exist which we do not perceive; yet we may not believe that any particular thing exists, without some reason for such belief: but I have no reason for believing the existence of matter."
-George Berkeley, Three Dialogues between Hylas and Philonous
He continues from this point, but I find little evidence besides his own justifications, which seem to be severely lacking. " Many things, for aught I know, may exist, whereof neither I nor any other man hath or can have any idea or notion whatsoever." would seem like a statement relating to the Kantian idea of noumena (and so I shall reference it as such). If he believes in noumena why does he find reason to justify a lack of faith in the nature of something to which he has no access or knowledge (to which he also admits, as Kant also has). Does he have other sources to better explain/justify his beliefs?