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Logic II 58

{Section title: Rough Definitions of the Categories of Groups of Sciences.}

The first great division of science will be according to
its fundamental purpose, making what I shall term Branches
of science. A modification of a purpose general purpose
may constitute a sub-branch. All knowledge whatever comes
from observation, but different sciences are observational in
such radically different ways that a kind of information derived
from the observation of one department of science (say Natural History) could not
possibly afford the information requiired of observation by
another branch (say mathematics.) I call groups based on
such considerations Classes, and modifications of the
same nature Subclasses. Observation is, in Agassiz's
phrase, the "ways and means" of attaining the purposes
of science. Of two departments of science A and B of the same
Class, A may derive special facts from B, for further generalization, while supplying
B with principles which the latter, not aiming so high, is
glad to have supplied find ready-made. A will rank higher
than B, by virtue of the greater generality of its object, while