Abstract: This is mostly trivia; but, reference to it is made elsewhere, so may as good put it up. Besides, it's oblique support of "rationality" against the converse.

Bishop George Berkeley's supposedly incontrovertible idealism, can be undone as follows:

Berkeley maintains, in essence, that all human perceptions are subsets of the perceptions of the deity, by whose will all perceptions are effectuated, and comport with one another to create the phenomenal world. And, the benevolence and omnipotence of the deity taken as given, perceptions can be relied upon as reality of that phenomenal world, forever after.

This scheme is objected to as, per the admission of the unrestricted Law of the Excluded Middle, either the deity perceives itself, or it does not.

But, if the deity perceives itself, in sensory fashion, yet humans do not. That being so, the lack, is by assumption from the will of the divine, that it be not perceived. However, then, by will also, the deity could at-once deprive of human perception any-thing; that is, it could exclude from perception anything it wishes, at its will. 

This being so, however, the deity surely cannot be relied upon to maintain the phenomenal world inviolate, since, rather, it might be altered in any way whatever for reasons humans cannot ken, and, if thoughts make up our minds, and thoughts derived from imitation or impression of sense-objects, our minds cannot be relied upon to subsist for any term of time. And, that being so, it cannot be guaranteed that Berkeley's mind, nor any other, can be relied upon to reason, or to have the reason sustain. So that, as guarantor of the phenomenal world, the deity cannot be relied upon so to sustain (nor the arguments of Berkeley's thoughts subsist; that they do and will ever-after implies, the deity cannot alter them, contrary to the assumption of its omnipotence).

Converse proposition, that the deity cannot perceive itself. However, in this case, there are limits to the deity’s perceptions, and so, whatever may subsist in even the phenomenal world, deity cannot be relied upon to perceive, nor to transmit such perceptions to humankind - so that, again, the deity cannot be relied upon to furnish for humans the unerring perceptual data of the phenomenal world.

Amusingly, David Hume's skepticism as to sensory data - essentially, agreeing with Berkeley that our sense data is furnished for us by the mind, but excepting only that Hume makes provision for no divinity, is even more readily dispatched.

To whit: Hume suggests his living quarters come into being - or at least, he only knows them to be in being - upon his viewing them, so he is as well to suppose his vision brings them into being. But of course this is only a comic instance of sighted prejudice: if Hume extends his hand behind, and raps at the wall - how comes the wall to be there to receive his knuckles? Or, again, if his knuckles in fact bring forth the wall: why so? How so, and why only just at point of impact there, and by his perception, the same point of impact each time? And how is it felt texture should comport with sighted expectation of texture? 

Moreover, that he feels the wall to be as far from his body each time, why should not the wall be ever either further or nearer; if his consciousness of it is only incidental - how is it he should remember the wall to repeat the experiment; how to recall the experiment? Or, if all these are in his own mind, created therein, rather than in the divinity - then fact the wall is(ital.) there in his mind all the time - just as if it did have all the while an existence entirely separate from his.

Observe well also, that it is Hume to whom (hm) we have to give thanks for the skepticism of the concept of causality. We can, with him well-dispensed, tend to restore that notion, cf. the essay here "Contra-Wittgenstein".

And to draw short the matter, if as in idealism the mind creates reality, and yet the mind exists so to know, the mind must have created itself or not, and, if the mind creates reality, it only could create itself. But if it does not create itself, it existed already, and so too could other things, since then not all existence is from the mind. Or, if it creates itself - then as mind by hypothesis creates all, it could create a world apart from itself to bring itself into being; or rather, could conceive that such a thing as a world to bring it into being might be - in which case it no longer creates itself, or better, it need not create itself, contrary to hypothesis. Moreover if the mind creates itself it must have existed in order to create itself, prior to creating itself, and so, it does not create itself, so it cannot create that part of reality which is itself.

And finally, versus Kant's idealism: the mind provisioned with categories out of which it forms the world, then the mind could conceive of a sub-mind likewise equipped with all its categories - in which case it has created itself, but it is powerless to create otherwise - and this restriction likewise could be applied to its own creator, if any - so that the world of all is not in fact other than some categories' restriction. Ergo, there is no noumenal world, if that is beyond or without categories for perception. (For the layperson: the mind creating can only do so according to its inbuilt categories; it would be impossible for a deity to create except of or in those categories - so no omnipotent deity in a noumenal world holds, or rather, if it there exists, it is powerless to create except for phenomena). Conversely, the first mind need not have been constituted so restricted by categories - and its phenomenal world is not necessary, so need not occur to be perceived, so then the noumenal being need know nothing whatever of what the world is, but therefore, it would knows nothing but the categories it creates - but it has no phenomena perceived on which to base its categories, and so, its categories have no content - and such a category-unrestricted being cannot create a phenomenal world. Or if the noumenal being does perceive sufficient phenomena for content - but then contrary to hypothesis that part of it which perceives phenomena is restricted to categories to perceive so.

Or rather: suppose what creates categories does so noumenally; the intuitions from categories it does not create - as if anything creates them; if they are created, so as to be known, so from categories related to phenomena - so the intuitions and the phenomenal world they inhabit are contingent - are, in fact, accidents uncaused by the categories, since those by new hypothesis are noumenally created without reference to phenomena, and thoughts and sensations would be totally unconnected, contrary to Kant's assertion - and contrary to the observations of consciousness of sensory data and one's own thoughts, and particularly contrary to the operations of one's "gedankenwelt" as related in "Contra-Wittgenstein".

But all this is idealism, so it's a waste of time; probably a waste of time to read it, so sorry. Except, as formerly observed, this is again to do the impossible, so by it take heart. Not too much, though; certainly not someone else's.