ress of explanation, it was not so much by vitiating
the deductive method as by putting men off from exact inquiries. More to
our present purpose were the supposed cataclysms, or extraordinary
convulsions of the earth, a belief in which long hindered the progress
of Geology. Again, in Biology, Psychology, and Sociology many
explanations have depended upon the doctrine that any improvement of
structure or faculty acquired by an individual may be inherited by his
descendants: as that, if an animal learns to climb trees, his offspring
have a greater aptitude for that mode of life; that if a man tries to be
good, his children find it easier to be virtuous; that if the
inhabitants of a district carry on cloth-work, it becomes easier for
each successive generation to acquire dexterity in that art. But now the
inheritability of powers acquired by the individual through his own
efforts, is disputed; and, if the denial be made good, all such
explanations as the above must be revised.

If, then, the premises of a deductive argument be vitiated in any of
these four ways, its conclusion will fail to agree with the results of
observation and experiment, unless, of course, one kind of error happen
to be cancelled by another that is 'equal and opposite.' We now come to
a variation of the method of combining Induction with Deduction, so
important as to require separate treatment.

Sec. 5. The Inverse or Historical Method has of late years become
remarkably fruitful. When the forces determining a phenomenon are too
numerous, or too indefinite, to be combined in a direct deduction, we
may begin by collecting an empirical law of the phenomenon (as that 'the
democracies of City-States are arbitrary and fickle'), and then
endeavour to show by deductions from "the nature of the case," that is,
from a consideration of the circumstances and forces known to be
operative (of which, in the above instance, the most important is
sympathetic contagion), that such a law was to be expected. Deduction is
thus called in to verify a previous induction; whereas in the 'Physical
Method' a deduction was verified by comparing it with an induction or an
experiment; hence the method now to be discussed has been named the
Inverse Deductive Method.

But although it is true that, in such inquiries as we are now dealing
with, induction generally takes the lead; yet I cannot think that the
mere order in which the two logical processes occur is the essential
dist