and his own personal observations: whereby each of his ideas rests
directly or indirectly on a basis of observation, which alone gives it
any real value; and likewise he is able to place every observation that
he makes under the right idea corresponding to it.

_Maturity_ of knowledge is the work of experience alone, and
consequently of time. For the knowledge we acquire from our own
observation is, as a rule, distinct from that we get through abstract
ideas; the former is acquired in the natural way, while the latter comes
through good and bad instruction and what other people have told to us.
Consequently, in youth there is generally little harmony and connection
between our ideas, which mere expressions have fixed, and our real
knowledge, which has been acquired by observation. Later they both
gradually approach and correct each other; but maturity of knowledge
does not exist until they have become quite incorporated. This maturity
is quite independent of that other kind of perfection, the standard of
which may be high or low, I mean the perfection to which the capacities
of an individual may be brought; it is not based on a correspondence
between the abstract and intuitive knowledge, but on the degree of
intensity of each.


The most necessary thing for the practical man is the attainment of an
exact and thorough knowledge of _what is really going on in the world;_
but it is also the most irksome, for a man may continue studying until
old age without having learnt all that is to be learnt; while one can
master the most important things in the sciences in one's youth. In
getting such a knowledge of the world, it is as a novice that the boy
and youth have the first and most difficult lessons to learn; but
frequently even the matured man has still much to learn. The study is of