the Catholic and Protestant Churches. A similar inconsistency appears in Locke, Berkeley, and
Hume.
In Locke, the inconsistency is still in the theory. We saw in an earlier chapter that Locke says, on
the one hand: "Since the mind, in all its thoughts and reasonings, hath no other immediate object
but its own ideas, which it alone does or can contemplate, it is evident that our knowledge is only
conversant about them." And: "Knowledge is the perception of the agreement or disagreement of
two ideas." Nevertheless, he maintains that we have three kinds of knowledge of real existence:
intuitive, of our own; demonstrative, of God's; and sensitive, of things present to sense. Simple
ideas, he maintains, are "the product of things operating on the mind in a natural way." How he
knows this, he does not explain; it certainly goes beyond "the agreement or disagreement of two
ideas."
Berkeley took an important step towards ending this inconsistency. For him, there are only minds
and their ideas; the physical external world is abolished. But he still failed to grasp all the
consequences of the epistemological principles that he took over from Locke. If he had been
completely consistent, he would have denied knowledge of God and of all minds except his own.
From such denial he was held back by his feelings as a clergyman and as a social being.
Hume shrank from nothing in pursuit of theoretical consistency, but felt no impulse to make his
practice conform to his theory. Hume denied the Self, and threw doubt on induction and
causation. He accepted Berkeley's abolition of matter, but not the substitute that Berkeley offered
in the form of God's ideas. It is true that, like Locke, he admitted no simple idea without an
antecedent impression, and no doubt he imagined an "impression" as a state of mind directly
caused by something external to the mind. But he could not admit this as a definition of
"impression," since he questioned the notion of "cause." I doubt whether either he or his disciples
were ever clearly aware of this problem as to impressions. Obviously, on his view, an
"impression" would have to be defined by some intrinsic character distinguishing it from an
"idea," since it could not be defined causally. He could not therefore argue that impressions give
knowledge of things external to ourselves, as had been done by Locke, and, in a modified form, by
Berkeley. He should, therefore, have believed him-