Both in his Principles of Human Knowledge, and in his Three Dialogues between Hylas and Philonous, Berkeley offers a variety of arguments against the view that there is a mind-independent, physical world.
Among them is an argument that he sets out in the Three Dialogues, and in which he tries to show not just that we do not have any adequate reason for believing that there are physical objects that can exist outside of any relation to a mind, but that the very idea of a physical object that exists independently of all relations to any mind involves a contradiction. This argument is contained in the following passage:
PHILONOUS: But (to pass by all that has been hitherto said, and reckon it for nothing, if you will have it so) I am content to put the whole upon this issue. If you can conceive it possible for any mixture or combination of qualities, or any sensible object whatever, to exist without the mind, then I will grant it actually to be so.
HYLAS: If it comes to that, the point will soon be decided. What more easy than to conceive a tree or house existing by itself, independent of, and unperceived by any mind whatsoever? I do at this present time conceive them existing after that manner.
PHILONOUS: How say you, Hylas, can you see a thing which is at the same time unseen?
HYLAS: No, that were a contradiction.
PHILONOUS: Is it not as great a contradiction to talk of conceiving a thing which is unconceived?
HYLAS: It is.
PHILONOUS: The tree or house therefore which you think of, is conceived by you?
HYLAS: How should it be otherwise?
PHILONOUS: And what is conceived, is surely in the mind?
HYLAS: Without question, that which is conceived is in the mind.
PHILONOUS: How then came you to say, you conceived a house or tree existing independent and out of all minds whatsoever?
HYLAS: That was I agree an oversight; but stay, let me consider what led me into it. – It is a pleasant mistake enough. As I was thinking of a tree in a solitary place, where no one was present to see it, I thought that was to conceive a tree as existing unperceived or unthought of, not considering that I myself conceived it all the while. But now I plainly see, that all I can do is to frame ideas in my own mind. I may indeed conceive in my own thoughts the idea of a tree, or a house, or a mountain, but that is all. And this is far from proving, that I can conceive them existing out of the minds of all spirits.
PHILONOUS: You acknowledge then that you cannot possibly conceive, how any one corporeal sensible thing should exist otherwise than in a mind.
HYLAS: I do.
Is the argument offered by Philonous sound? In order to discuss this question, try to set out Philonous’s argument in a careful, step by step fashion, numbering each step, and indicating which steps are premises, and which are conclusions that are supposed to follow from earlier steps. Then, if you think that the argument is basically sound, set out what you think are the one or two most important objections to the argument, and indicate, in each case, what you take to be a plausible response. Alternatively, if you think that the argument is unsound, describe, in a careful and detailed fashion, what you take to be the central flaw in the argument, and defend your view against possible objections. This is a tricky argument to evaluate unless you are familiar with the distinction in philosophy of language between extensional and intensional contexts. So if you would like to tackle this topic, but are not familiar with that distinction, please read the relevant handout on the class web site, and talk to me about anything that is unclear.