treats the first principles of Contradiction and Causation as true of
things so far as they are known to us, and not merely as conditions or
tendencies of thought; and it takes these principles as conditions of
right thinking, because they seem to hold good of Nature and human life.

To these differences of opinion it will be necessary to recur in the
next chapter (§ 4); but here I may observe that it is easy to exaggerate
their importance in Logic. There is really little at issue between
schools of logicians as such, and as far as their doctrines run
parallel; it is on the metaphysical grounds of their study, or as to its
scope and comprehension, that they find a battle-field. The present work
generally proceeds upon the third, or Materialist doctrine. If Deduction
and Induction are regarded as mutually dependent parts of one science,
uniting the discipline of consistent discourse with the method of
investigating laws of physical phenomena, the Materialist doctrine, that
the principles of Logic are founded on fact, seems to be the most
natural way of thinking. But if the unity of Deduction and Induction is
not disputed by the other schools, the Materialist may regard them as
allies exhibiting in their own way the same body of truths. The
Nominalist may certainly claim that his doctrine is indispensable:
consistently cogent forms of statement are necessary both to the
Conceptualist and to the Materialist; neither the relations of thought
nor those of fact can be arrested or presented without the aid of
language or some equivalent system of signs. The Conceptualist may urge
that the Nominalist's forms of statement and argument exist for the sake
of their meaning, namely, judgments and reasonings; and that the
Materialist's laws of Nature are only judgments founded upon our
conceptions of Nature; that the truth of observations and experiments
depends upon our powers of perception; that perception is inseparable
from understanding, and that a system of Induction may be constructed