a very long time
finding out, but which we can now realize without a great deal of
explanation. These general truths, we may say, are preliminary to the
story itself; they deal rather with the need of defining, first of
all, the subject or topic of which the story is to be told.

1. The first such truth is that the mind is not the possession of man
alone. Other creatures have minds. Psychology no longer confines
itself, as it formerly did, to the human soul, denying to the animals
a place in this highest of all the sciences. It finds itself unable to
require any test or evidence of the presence of mind which the animals
do not meet, nor does it find any place at which the story of the mind
can begin higher up than the very beginnings of life. For as soon as
we ask, "How much mind is necessary to start with?" we have to answer,
"Any mind at all"; and all the animals are possessed of some of the
actions which we associate with mind. Of course, the ascertainment of
the truth of this belongs--as the ascertainment of all the truths of
nature belongs--to scientific investigation itself. It is the
scientific man's rule not to assume anything except as he finds facts
to support the assumption. So we find a great department of psychology
devoted to just this question--i.e., of tracing mind in the animals
and in the child, and noting the stages of what is called its
"evolution" in the ascending scale of animal life, and its
"development" in the rapid growth which every child goes through in
the nursery. This gives us two chapters of the story of the mind.
Together they are called "Genetic Psychology," having two divisions,
"Animal or Comparative Psychology" and "Child Psychology."

2. Another general truth to note at the outset is this: that we are
able to get real knowledge about the mind. This may seem at first
sight a useless question to raise, seeing that our minds are, in the
thought of many, about the only things we are really sure of. But that
sort of sureness is not what science seeks. Every science requires
some means of investigation, some method of procedure, which is more
exact than the mere say-so of common sense; and which can be used over
and again by different investigators and under different conditions.
This gives a high degree of verification and control to the results
once obtained. The chemist has his acids, and reagents, and blowpipes,
etc.; they constitute his instruments, and by using them, under
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