Berkeley's Master Argument against Material Substance
Much of Berkeley’s argument against matter is direcetd against represenational realism, i.e., against
the view that we directly perceive ideas but these ideas are caused by external physical substances.
But he also argues against the view that we directly perceive material objects themselves.
Here is the relevant passage from the Three Dialogues:
Phil: . . . If you can conceive it to be possible froany mixture or combination of qualities, or any
sensible object whatever, to exist outside the mind, then I will grant it actually to be so.
Hyl: By that test, the point will soon be decided.What is easier than to conceive a tree or house
existing by itself, independently of and unperceived by any mind whatsoever? I conceive them
existing in that way right now.
Phil: Tell me, Hylas, can you see a thing which is at the same time unseen?
Hyl: No, that would be a contradiction.
Phil: Is it not as great a contradiction to talk of conceiving a thing which is unconceived?
Hyl: It is.
Phil: The tree or house therefore which you think of is conceived by you.
Hyl: How could it be otherwise?
Phil: And what is conceived is surely in the mind.
Hyl: Without question, what is conceived is in the mind.
Phil: Then what led you to say that you conceivd ea house or tree existing independently and out
of all minds whatsoever?
Hyl: That was an oversight, I admit; . . . (Bennett, p. 21).
Here Philonous (speaking for Berkeley) contends that we cannot conceive of mind-independent
objects, i.e., objects existing unperceived and unthought of. The reas on that we cannot is that in
order to think about something, we must ourselves be thinking about it.
We can formulate Berkeley’s reasoning as follows:
1. If we can conceive of a tree existing inde pendently of any mind whatsoever, then wecan
conceive of the tree existing unconceived.
2. It is a contradiction to suppose that we can conceive of something that is unconceived.
3. We cannot conceive of a tree (or anything else) existing independent and out of all minds.
The key idea in this argument is that
It is a contradiction to suppose that we can conceive of a thing that is unconceived.
The reason that this supposed to be a contradiction isthat in order to conceive of any such thing, we
must ourselves be conceiving, i.e., thinking, of it. The problem however is that the phrase
we can conceive of a thing that is unconceived
is ambiguous: taken one way, it is indeed contradictory; taken in another way it is not. So,
Berkeley’s argument rests on that ambiguity.
Consider the claim
we can conceive of a tree that exists unconceived.
This is susceptible of wo possible interpretations:
(A) It is possible for us tothink that there is some tree (or other) about which no one is thinking.
(B) It is possible for us to think, concerningsome particular tree, that no one is thinking about
(B) is certainly false and contradictory: If we think, concerning x, that no one is thinking about x,
then we are thinking about x. Hence, it is impossible for there to be a tree concerning which we
think no one is thinking: if there were such aetre it would be one about which someone was thinking
and no one was thinking. This would indeed be a contradiction.
But it does not follow from this that (A) is false and contradictory. In fact, (A) is exactly what a
realist believes, namely, as Hylas puts it, that to exist is one thing, and to be perceived is another.
Accordingly, the two premises of the Master Argument are ambiguous. Each is true on one way of
interpreting the phrase “we can conceive of a tree that exists unconceived” and false on the other.
But there is no consistent interpretation that makes both true.