re knowledge of our own minds than those of animals, and that we
should use this knowledge to infer the existence of something similar
to our own mental processes in animals and even in plants. On the other
hand, it may be held that animals and plants present simpler phenomena,
more easily analysed than those of human minds; on this ground it may be
urged that explanations which are adequate in the case of animals ought
not to be lightly rejected in the case of man. The practical effects of
these two views are diametrically opposite: the first leads us to level
up animal intelligence with what we believe ourselves to know about our
own intelligence, while the second leads us to attempt a levelling down
of our own intelligence to something not too remote from what we can
observe in animals. It is therefore important to consider the relative
justification of the two ways of applying the principle of continuity.

It is clear that the question turns upon another, namely, which can we
know best, the psychology of animals or that of human beings? If we
can know most about animals, we shall use this knowledge as a basis for
inference about human beings; if we can know most about human beings, we
shall adopt the opposite procedure. And the question whether we can know
most about the psychology of human beings or about that of animals turns
upon yet another, namely: Is introspection or external observation
the surer method in psychology? This is a question which I propose to
discuss at length in Lecture VI; I shall therefore content myself now
with a statement of the conclusions to be arrived at.

We know a great many things concerning ourselves which we cannot know
nearly so directly concerning animals or even other people. We know when
we have a toothache, what we are thinking of, what dreams we have when
we are asleep, and a host of other occurrences which we only know about
others when they tell us of them, or otherwise make them inferable
by their behaviour. Thus, so far as knowledge of detached facts is
concerned, the advantage is on the side of self-knowledge as against
external observation.

But when we come to the analysis and scientific understanding of the
facts, the advantages on the side of self-knowledge become far less
clear. We know, for example, that we have desires and beliefs, but we
do not know what constitutes a desire or a belief. The phenomena are so
familiar that it is difficult to realize how little we