Remember, things will be recalled as they were impressed, so the value
of your ideas in reasoning will depend upon the manner in which you
make original impressions. A further characteristic of serviceable
ideas is clarity. Ideas are sometimes described as "clear" in
opposition to "muddy." You know what is meant by these distinctions,
and you may be assured that one cause for your failures in reasoning is
that your ideas are not clear. This manifests itself in inability to
make clear statements and to comprehend clearly. The latter condition
is easily illustrated. When you began the study of geometry you faced a
multitude of new terms; we call them technical terms, such as
projection, scalene, theory of limits. These had to be clearly
understood before you could reason in the subject. And when, in the
progress of your study, you experienced difficulty in reasoning out
problems, it was very likely due to the fact that you did not master
the technical terms, and as soon as you encountered the difficulties of
the course, you failed because your foundation laying did not involve
the acquisition of clear ideas. Examine your difficulties in reasoning
subjects and if you find them traceable to vagueness of ideas, take
steps to clarify them.

Ideas may be clarified in two ways: by definition and by
classification. Definition is a familiar device, for you have had much
to do with it in learning. The memorization of definitions is an
excellent practice, not as an end in itself, but as a means to the end
of effective reasoning. Throughout your study, then, pay much attention
to definitions. Some you will find in your texts, but others you will
have to make for yourself. In order to get practice in this, undertake
the manufacture of a few definitions, using terms such as charity,
benevolence, natural selection. This exercise will reveal what an
exacting mental operation definition is and will prove how vague most of