constant use of hypotheses as an aid to investigation. What hypotheses
may one frame, and what are inadmissible? How important an
investigation of this question may be to the worker in certain branches
of science will be clear to one who will read with attention Professor
Poincaré's brilliant little work on "Science and Hypothesis." [2]

There is no field in art, literature, or science in which the work of
the critic is wholly superfluous. "There are periods in the growth of
science," writes Professor Pearson in his deservedly popular work, "The
Grammar of Science," [3] "when it is well to turn our attention from
its imposing superstructure and to examine carefully its foundations.
The present book is primarily intended as a criticism of the
fundamental concepts of modern science, and as such finds its
justification in the motto placed upon its title-page." The motto in
question is a quotation from the French philosopher Cousin: "Criticism
is the life of science."

We have seen in Chapter XVI that a work on logic may be a comparatively
simple thing. It may describe the ways in which men reason when they
reason correctly, and may not go deep into metaphysical questions. On
the other hand, it may be deeply metaphysical.

When we approach the part of logic which deals with the principles and
methods of the sciences, this difference is forced upon our attention.
One may set forth the assumptions upon which a science rests, and may
describe the methods of investigation employed, without going much
below the plane of common thought. As a type of such works I may
mention the useful treatise by Professor Jevons cited earlier in this
chapter.