mind is able, however, to reject these irrelevant ideas, and
select only those that seem to adjust themselves to the problem in hand.
The cause of this lies in the fact that the problem is at the outset at
least partly understood by the learner, which fact enables him to
determine whether the ideas coming forward in consciousness are related
in any way to this partially known topic. Thus in the example cited,
the learner knows the problem sufficiently to realize that it is a
question of grammatical function, and is able, therefore, to feel the
value, or suitability, of any knowledge which may be applied to it, even
before he is fully aware of its ultimate relation thereto.

LAW OF PREPARATION

=Control of Old Knowledge Necessary.=--But notwithstanding the direction
given the apperceptive process through the aim, or problem, it is
evident that if the pupil is to select from his former experiences the
particular elements which bear upon the problem in hand, he must have a
ready and intelligent control over such former knowledge. It is too
evident, however, that pupils frequently do not possess sufficient
control over the old knowledge which will bear upon a presented problem.
In endeavouring, for example, to grasp the relation of the exterior
angle to the two interior and opposite angles, the pupil may fail
because he has not a clear knowledge of the equality of angles in
connection with parallel lines. For this reason teachers will often find
it necessary (before bringing old knowledge to bear upon a new problem)
to review the old knowledge, or experience, to be used during the
apperceptive process. Thus a lesson on the participle may begin with a
review of the pupils' knowledge of verbs and adjectives, a lesson on the
making of the colours orange and green for painting a pumpkin with its
green stem may begin with a recognition of the standard colours, red,
yellow, and blue, and the writing of a capital letter with a review of
certain movements.

=Preparation Recalls Interpreting Ideas.=--It must be noted that this
review of former knowledge always implies, either that the pupil is
likely to have forgotten at least partially this former knowledge, or
that without such review he is not likely to recall and apply it readily
when the new problem is placed before him. For this reason the teacher
is usually warned that his lesson should always begin with a review of
such of the pupil's old knowledge as is to be used in ma