alue of an analogical argument depends on
the extent of ascertained resemblance as compared, first, with the
amount of ascertained difference, and next, with the extent of the
unexplored region of unascertained properties.

The conclusions of analogy are not of direct use, unless when the case
to which we reason is a case _adjacent_, not, as before, in time or
place, but in _circumstances_. Even then a complete induction should be
sought after. But the great value of analogy, even when faint, in
science, is that it may suggest observations and experiments, with a
view to establishing positive scientific truths, for which, however, the
hypotheses based on analogies must never be mistaken.

CHAPTER XXI.

THE EVIDENCE OF THE LAW OF UNIVERSAL CAUSATION.

The validity of all the four inductive methods depends on our assuming
that there is a cause for every event. The belief in this, i.e. in the
law of universal causation, some affirm, is an instinct which needs no
warrant other than all men's disposition to believe it; and they argue
that to demand evidence of it is to appeal to the intellect from the
intellect. But, though there is no appeal from the faculties all
together, there may be from one to another: and, as belief is not proof
(for it may be generated by association of ideas as well as by
evidence), a case of belief does require to be proved by an appeal to
something else, viz. to the faculties of sense and consciousness.

The law of universal causation is, in fact, a generalisation from many
partial uniformities of sequence. Consequently, like these, which cannot
have been arrived at by any strict inductive method (for all such
methods presuppose the law of causation itself), it must itself be based
on inductions _per simplicem enumerationem_, that is, generalisations of
observed facts, from the mere absence of any known instances to the
contrary. This unscientific process is, it is true, usually delusive;
but only because, and in proportion as, the subject-matter of the
observation is limited in extent. Its results, whenever the number of
coincidences is too large for chance to explain, are empirical laws.
These are ordinarily true only within certain limits of time, place, and
circumstance, since, beyond these, there may be different collocations
or counteracting agencies. But the subject-matter of the law of
universal causation is so diffused that there is no time, place, or set
of circumstances, at