bles him to read into it two ideas, three-sidedness and
three-angledness, and only these factors, therefore, organize themselves
into his experience triangle. Nor would any amount of mere attention
enable him at this stage to discover another important quality in the
thing triangle. Later, however, through the growth of his geometric
experience, he may be able to read another quality into a triangle,
namely two-right-angledness. This new quality will then, and only then,
be organized with his former knowledge into a more complete knowledge of
a triangle. Here again it is seen that analysis as a learning process is
really reading into a new presentation something which the mind already
possesses as an element of former experience, and not gaining something
at first hand out of the presented problem.

=Problem Directs Selection.=--It will be well to note here also that the
selecting of the interpreting ideas is usually controlled by the problem
with which the mind is engaged. This is indicated from the various ways
in which the same object may be interpreted as the mind is confronted
with different problems. The round stone, for instance, when one wishes
to crack the filbert, is viewed as a hammer; when he wishes to place his
paper on the ground, it becomes a weight; when he is threatened by the
strange dog, it becomes a weapon of defence. In like manner the sign _x_
suggests an unknown quantity in relation to the algebraic problem; in
relation to phonics it is a double sound; in relation to numeration, the
number ten. It is evident that in all these cases, what determines the
meaning given to the presented object is the _need_, or _problem_, that
is at the moment predominant. In the same way, any lesson problem, in so
far as it is felt to be of value, forms a starting-point for calling up
other ideas, and therefore starts in the learner's mind a flow of ideas
which is likely to furnish the solution. Moreover, the mind has the
power to measure the suitability of various ideas and select or reject
them as they are felt to stand related to the problem in hand. For
example, when a pupil is engaged in a study of the grammatical value of
the word _driving_ in the sentence, "The boy driving the horse is very
noisy," it is quite possible that he may think of the horse at his own
home, or the shouting of his father's hired man, or even perhaps the
form of the word _driving_, if he has just been viewing it in a writing
lesson. The