aterial Cause, the sources of his material, and the Formal Cause,
the reason why he shaped it as he did. In the case of Mill's system
we have to ask: What first moved him to formulate the methods of
scientific investigation? Whence did he derive his materials? Why
did he give his scientific method the form of a supplement to the old
Aristotelian Logic? We cannot absolutely separate the three inquiries,
but motive, matter and form each had a traceable influence on the
leading features of his System.

First, then, as to his motive. It is a mistake to suppose that Mill's
object was to frame an organon that might assist men of science as
ordinarily understood in making discoveries. Bacon, his secretary
tells us, was wont to complain that he should be forced to be a
Workman and a Labourer in science when he thought he deserved to be an
Architect in this building. And men of science have sometimes rebuked
Mill for his presumption in that, not being himself an investigator
in any department of exact science, he should volunteer to teach them
their business. But Mill was really guilty of no such presumption. His
object, on the contrary, was to learn their method with a view to
its application to subjects that had not yet undergone scientific
treatment. Briefly stated, his purpose was to go to the practical
workers in the exact sciences, Astronomy, Chemistry, Heat, Light,
Electricity, Molar and Molecular Physics; ascertain, not so much how
they made their discoveries as how they assured themselves and others
that their conclusions were sound; and having ascertained their tests
of truth and principles of proof, to formulate these tests so that
they might be applied to propositions outside the range of the exact
sciences, propositions in Politics, Ethics, History, Psychology.
More particularly he studied how scientific men verify, and when
they accept as proved, propositions of causation, explanations of
the causes of things. In effect, his survey of scientific method was
designed to lead up to the Sixth Book in his System, the Logic of the
Moral Sciences. There are multitudes of floating endoxes or current
opinions concerning man and his concerns, assigning causes for the
conduct and character of individuals and of communities. Mill showed
himself quite aware that the same modes of investigation may not be
practicable, and that it may not be possible, though men are always
ready to assign causes with confidence, to ascertain caus