The second characteristic pertains to their _narrowness_ and
consequent _definiteness_. They call in each case for an investigation
of a relatively small and definite topic. This can be further seen
from the following topics in Biology: What household plants are most
desirable? How can these plants be raised? What are their principal
enemies, and how can these best be overcome? Whether we be working on
one or more of such problems at a time, they are so specific that we
need never be confused as to what we are attempting.

The nature of these aims in study can be made still clearer by
contrasting them with others that are very common. The "harmonious
development of all the faculties," or mental discipline, for instance,
has long been lauded by educators as one chief purpose in study.
Agassiz was one such educator, and in his desire to cultivate the
power of observation, he is said to have set students at work upon the
study of fishes without directions, to struggle as they might. Many
teachers of science before and since his time have followed a similar
method. Truth for truth's sake, or the idea that one should study
merely for the sake of knowing, has often been associated with mental
discipline as a worthy end. Culture is a third common purpose.

Each of these aims, instead of originating in the particular interests
of the individual, is reached by consideration of life as a whole, and
of the final purposes of education. They are too general in nature to
recognize individual preferences, and they are also too general to
cause much discrimination in the selection of topics and of particular
facts within topics. Strange to say, however, they have discriminated
against the one kind of knowledge that the aforementioned specific
aims emphasize as especially desirable. Under their exclusive
influence, for example, students of biology have generally made an