his hypothetical case to show the extreme difficulty of
reaching anything more than hypotheses by _a priori_ reasoning. We have
a certain number of fairly well established general principles in
secondary education. Perhaps those most frequently employed are our
generalizations regarding adolescence and its influences upon the mental
and especially the emotional life of high-school pupils. Stanley Hall's
work in this field is wonderfully stimulating and suggestive, and yet we
should not forget that most of his generalizations are, after all, only
plausible hypotheses to be acted upon as tentative guides for practice
and to be tested carefully under controlled conditions, rather than to
be accepted as immutable and unchangeable laws. We sometimes assume that
all high-school pupils are adolescents, when the likelihood is that an
appreciable proportion of pupils in the first two years have not yet
reached this important node of their development.

I say this not to minimize in any way the importance that attaches to
adolescent characteristics, but rather to suggest that you who are daily
dealing with these pupils can in the aggregate add immeasurably to the
knowledge that we now have concerning this period. A tremendous waste is
constantly going on in that most precious of all our possible
resources,--namely, human experience. How many problems that are well
solved have to be solved again and again because the experience has not
been crystallized in a well-tested fact or principle; how many
experiences that might be well worth the effort that they cost are quite
worthless because, in undergoing them, we have neglected some one or
another of the rules that govern inexorably the validity of our
inferences and conclusions. That is all that the scientific method means
in the last analysis: it is a system of principles that enable us to
make our experience worth while in meeting later situations. We all
have the opportunity of contributing to the sum total of human
knowledge, if only we know the rules of the game.

I said that one way of solving these subordinate problems that arise in
the realization of our chief aims in teaching is the _a priori_ method
of applying general principles to the problems. Another method is to
imitate the way in which we have seen some one else handle the
situation. Now this may be the most effective way possible. In fact, if
a sufficient number of generations of teachers keep on blindly plunging
i