remains to us as the main source of the knowledge we possess, or can
acquire, respecting the conditions and laws of recurrence of the more
complex phenomena, is called, in its most general expression, the
deductive method, and consists of three operations: the first, one of
direct induction; the second, of ratiocination; and the third, of
verification."

Now, the conditions which have determined the existence of species are
not only exceedingly complex, but, so far as the great majority of them
are concerned, are necessarily beyond our cognizance. But what Mr.
Darwin has attempted to do is in exact accordance with the rule laid
down by Mr. Mill; he has endeavoured to determine certain great facts
inductively, by observation and experiment; he has then reasoned from
the data thus furnished; and lastly, he has tested the validity of his
ratiocination by comparing his deductions with the observed facts of
Nature. Inductively, Mr. Darwin endeavours to prove that species arise
in a given way. Deductively, he desires to show that, if they arise in
that way, the facts of distribution, development, classification, etc.,
may be accounted for, 'i.e.' may be deduced from their mode of origin,
combined with admitted changes in physical geography and climate, during
an indefinite period. And this explanation, or coincidence of
observed with deduced facts, is, so far as it extends, a verification
of the Darwinian view.

There is no fault to be found with Mr. Darwin's method, then; but it is
another question whether he has fulfilled all the conditions imposed by
that method. Is it satisfactorily proved, in fact, that species may be
originated by selection? that there is such a thing as natural
selection? that none of the phenomena exhibited by species are
inconsistent with the origin of species in this way? If these