20. Berkeley's statement that spirit cannot itself be perceived
but only by the effects that it produces would, if taken seriously,

  ― 38. ―
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imply that we really had no knowledge of spirit. He says that we
have some notion of spirit and of its various operations such as
willing, living, hating and so on as is indicated by the fact that
we understand the meaning of these words, (XXVII) but this understanding
cannot be arrived at in the same way as understanding of
terms such as colours, extension and so forth. Now if this were so
we should really require to have different forms of expression for
the different kinds of objects which we could conceive. But actually
we have the same forms of expression; we make statements in the same
propositional form about the supposedly active things and the passive
things. We say that we have some conception of them both, and we make
statements of the form “I a willing”, or “The apple is green”, showing
that we treat the two as having the same sort of reality and the same
conditions of existence; so that it is impossible logically to work out
any theory in which types of existence are distinguished. Unless a
mind and an idea are taken as existing in the same way; unless, that is
to say, each of them is an independent thing, then no account of such
relations between them as “knowing” or “causing” can be given; if the
mind causes something that must be something real or else no real
causing has taken place, and similarly if the mind knows something.

But, working on the basis of the distinction between active
spirit and passive ideas, Berkeley attempts to account for that scientific
knowledge which we actually possess; to account, in particular, for
the fact that there can be true theories and false theories about the
things which are perceived. As far as the notion of ideas is concerned,
the notion, that is, of things existing by their being known, it would
appear that there can be no such thing as error. But Berkeley tries
to account for error by distinguishing between ideas of sensation
and ideas of reflection. (XXIX) The distinction is made primarily
by reference to the effects that a given mind can produce; a man can
influence his own thoughts to a certain extent, but when he looks
around him and receives sensations he cannot determine what these
sensations shall be; he cannot, in fact, perceive whatever he likes, but
has to accept what is impressed on his mind. And so Berkeley says
that, while the ideas of reflection or images are caused by the mind
in which they occur, the ideas of sensation must be caused by some
other mind.

Now strictly in terms of the theory of ideas this distinction
could not be made. If I think of a certain idea as being caused by me,
then “being caused by me” is another idea which accompanies the former
but which, on Berkeley's own showing, cannot enter into it without being
absolutely identified with it so that the statement that the idea is
caused by me would have no meaning. But if the ideas are separate, then
likewise an idea of sensation and the idea of its not being caused by
me are also separate, and we cannot account for the proposition whereby
one is asserted of the other. But even if they are separate, still
they are both in the mind which has them and they can entitle it to
draw no conclusion as to what exists outside that mind whether this
is said to be another mind or not. Thus in either case, whether we have
four ideas, the image, the idea of being caused by me, the sensation and
the idea of not being caused by me, or only the two, image and sensation---the
supposed predicates of these two being really identical
with their essence, we have no justification for making the distinction
between sensation and reflection or imagination; the ideas may differ
qualitatively from one another but they must all belong to the very
same order. On the other hand, if we recognise propositions of the

  ― 39. ―
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kind formulated by Berkeley that certain things are caused by me
and certain other things are not caused by me, then we are recognising
the possibility of error even as regards what was supposed to
be in our minds; and, in recognising that possibility, we are at the
same time recognising that there are objective truths, truths, that is,
which are not dependent on being known for their being true; or, in
other words, the recognition of propositions is in contradiction to the
doctrine of essences because it shows that things have particular
features and that we are not entitled to demand that they should be
known completely if they are to be known at all. And in thus recognising
relations among things we are recognising that what is perceived
by us need not be constituted by that perception.

Berkeley goes on to make a further distinction between ideas
of sense and ideas of imagination, namely, that the former “are more
strong, lively, and distinct than than those of the imagination” the latter,
and that they have likewise a greater steadiness, order and coherence,
that they occur according to set rules or established methods, and that
these rules, according to which the mind external to us excites ideas
in us, are the laws of nature. (XXX) It is the business of science,
therefore, to discover the laws of nature, that is, the order in which
sensations occur. Now here again Berkeley is making distinctions which
are not in accordance with the doctrine of simple ideas and the criticism
of which applies also to Hume who makes similar distinctions.
He says, in the first place, that the ideas of sense are distinct and
lively in comparison with those of imagination. But, according to his
view, distinctness and liveliness ought to be separate ideas; they ought
not to be qualities of given ideas because these ideas have one complete
nature which is given all at once. And the same applies to the relations
which he affirms hold among those ideas; that is, if we can speak
of a certain order, then that order ought to be a particular idea of
the same sort as others, and when we say, for example, that the idea A
precedes the idea B, what we really have is not a relation between one
idea and another but three separate ideas, A, preceding, and B. If, on the
other hand, we admit that A really does precede B, then we are speaking
about something which has actual existence and not merely relative
existence. And, again, if there is a set order in which ideas of sensation
occur, then it would still seem that error would be impossible. It
would seem to be possible only if we can confuse between images and
sensations; only, that is, if we can suppose that something which was
caused by us was, in reality, not caused by us or vice versa. But in
the first place this implies that we do not have intuitive and certain
knowledge of our own operations, and in the second place, the same argument
could be applied to the case of perception and we should have
to admit that what was actually perceived by us might mistakenly be
supposed not to have been perceived by us. The main objection is that
which is concerned with order which, in itself, implies that we are
dealing with actually existing things which have various features and
various relations to one another.