Philosopher George Berkeley’s short book Three Dialogues Between Hylas and Philonous is an interesting read that, I think, has some merit to it. For one thing, Berkeley correctly understands that there is nothing in the created universe that has “self-existence,” for self-existence is attributable only to God. Also, his criticism of the supposed existence of “matter” is helpful in underscoring the absurdity of materialism, when drawn to its logical conclusions. What is problematic about his conclusion, viz. Nothing exists outside of the mind of the perceiving spirit, however, is that it leaves the reader without any certain means of differentiating between “sense ideas” (i.e. real ideas sensed by the perceiving subject) and “ideas of the imagination” (i.e. ideas that are constructed by the mind and are not conveyed via sensation).
The following quotation is Philonous’ (i.e. the character in Berkeley’s dialogue that represents Berkeley’s philosophy) response to Hylas’ inquiry – “…how, according to your views, do real things differ from chimeras formed by the imagination or the visions of a dream, since according to you they are all equally in the mind?”
Phil: The ideas formed by the imagination are faint and indistinct; also, they are entirely dependent upon the will. But the ideas perceived by sense — that is, real things — are more vivid and clear, and don’t in that way depend on our will, because they are imprinted on our mind by a spirit other than us. So there’s no danger of mixing up these real things with the foregoing ideas formed by the imagination, and equally little danger of failing to distinguish them from the visions of a dream, which are dim, irregular, and confused. And even if dreams were lively and natural, they could be distinguished from realities by their not being coherently connected with the preceding and subsequent episodes of our lives. In short, whatever method you use to distinguish things from chimeras is obviously available to me too. For any method must, I presume, be based on some perceived difference, and I don’t want to deprive you of any one thing you perceive.
Here is the problem with Philonous’ reply:
It begs the question.
In other words, arguing that the perception of a difference between one thing and another constitutes a reliable means of differentiating reality from fantasy is circular reasoning. Such a “solution” merely removes the problem by a step. Upon what authority can Philonous say that the perception of a difference (or many differences, for that matter) between what is real and what isn’t is a correct means of differentiating reality from fantasy?
What would Philonous say of a paranoid schizophrenic?
What would Philonous say of an insomniac who cannot differentiate between days of the week, real experiences and dreams, real events and distorted memories of those events, etc?
There is no way, on Philonous’ account, to divide reality from fantasy without arguing in a circle.
What is more destructive of Berkeley’s dubious distinction, however, is the fact that he later criticizes strict conceptions of identity. Yet without an absolutely strict distinction between the real and the fantastical, Berkeley/Philonous cannot claim the capacity to differentiate between the two. To put this another way: Berkeley/Philonous repudiates strict conceptions of self-identity (e.g., in order for A to be identical to A, A must retain the same properties under all conditions), but at the same time rests upon a strict notion of identity (e.g., reality is x, whereas fantasy is y, and these are mutually exclusive).
If Berkeley/Philonous’ criticism of identity is correct, then it is improper to attempt to define reality and fantasy as strictly self-identical, i.e. entailing their mutual exclusivity. Yet if Berkeley/Philonous’ criticism of identity is incorrect, then his assumption that we can trust our sensations is also wrong.
Berkeley’s philosophy of immaterialism is intriguing and provides many useful critcisms of materialism, but due to these glaring errors cause his attempt to challenge the skepticism of his day to result, ironically, in an even more radical form of skepticism.