on. Some subjects, like the
social sciences, naturally allow for richer interpretations. Others,
like the languages and the physical sciences, present only very
limited opportunities; in the biological sciences the possibilities,
though not as rich as in the social sciences, are numerous and
productive of good results.

_Comparison_ is a second means of producing thoroughness of
comprehension. Good teaching abounds in comparisons which are
introduced at the end of every important topic rather than reserved
for examination questions. Comparisons used liberally at every logical
pause in the development of a subject always give an added viewpoint,
review early subject matter incidentally, stir thought, and make for
better organization. How much more clearly are the causes of the War
of 1812 understood after they are compared with those that brought on
the Revolutionary War! How much more definite are the causes of the
American Revolution when compared with those that brought on the
French Revolution! A writer, a school, or a movement in English
literature may be understood when studied by itself; but how is
comprehension deepened when each is compared with another writer or
school or movement! Comparison of perception and conception or
appreciation and association in psychology, makes each activity stand
out clearer in the mind of the student. Compare the laws of rent,
wage, profit, and interest in economics, and not only each is better
understood but the basic laws of distribution are readily derived by
the student. Similarly, comparisons in mathematics, physics,
chemistry, and the entire range of collegiate subjects give increased
comprehension, useful though incidental reviews, and greater
unification of knowledge, as well as added points of view.

_Correlation_ as a means of producing thoroughness is closely allied
to comparison. Correlation relates kindred topics of different
subjects, while comparison points out relations in the same subject.
The instructor who correlates the history of education with the
political and economic history that the student learned in another
course is unifying related experience, reducing the field of
knowledge, introducing logical organization, and adding new
interpretations to facts already acquired. Similarly, teaching must be
enriched by correlating physics and mathematics, chemistry and
physics, literature and music, history of literature and general
history, until instruction ha