if we ask, again, how any number of past experiments can prove a general
proposition, which must be good for the future as well as for the past,
the uniformity of causation is invoked; that is, appeal is made to a
principle, and that again is deductive proof. Induction then depends
upon Deduction.

We may put it in this way: Deduction depends on Induction, if general
propositions are only known to us through the facts: Induction depends
on Deduction, because one fact can never prove another, except so far as
what is true of the one is true of the other and of any other of the
same kind; and because, to exhibit this resemblance of the facts, it
must be stated in a general proposition.

§ 4. The use of Logic is often disputed: those who have not studied it,
often feel confident of their ability to do without it; those who have
studied it, are sometimes disgusted with what they consider to be its
superficial analysis of the grounds of evidence, or needless
technicality in the discussion of details. As to those who, not having
studied Logic, yet despise it, there will be time enough to discuss its
utility with them, when they know something about it; and as for those
who, having studied it, turn away in disgust, whether they are justified
every man must judge for himself, when he has attained to equal
proficiency in the subject. Meanwhile, the following considerations may
be offered in its favour:

Logic states, and partly explains and applies, certain abstract
principles which all other sciences take for granted; namely, the axioms
above mentioned--the principles of Contradiction, of the Syllogism and
of Causation. By exercising the student in the apprehension of these
truths, and in the application of them to particular propositions, it