ta. Suppose a person were
to institute a home for lost dogs, he would doubtless try to ascertain
how many dogs were likely to go astray, and in so doing would be
guided by statistics. But in judging of the probability of the
straying of a particular dog, he would pay little heed to statistics
as determining the chances, but would proceed upon empirical knowledge
of the character of the dog and his master. Even in betting on the
field against a particular horse, the bookmaker does not calculate
from numerical data such as the number of horses entered or the
number of times the favourite has been beaten: he tries to get at
the pedigree and previous performances of the various horses in the
running. We proceed by calculation of chances only when we cannot do
better.

[Footnote 1: _Empirical Logic_, p. 556.]

[Footnote 2: Mr. Jevons held that all inference is merely
probable and that no inference is certain. But this is a
purposeless repudiation of common meaning, which he cannot
himself consistently adhere to. We find him saying that if a
penny is tossed into the air it will _certainly_ come down
on one side or the other, on which side being a matter of
probability. In common speech probability is applied to a
degree of belief short of certainty, but to say that certainty
is the highest degree of probability does no violence to the
common meaning.]

CHAPTER X.

INFERENCE FROM ANALOGY.

The word Analogy was appropriated by Mill, in accordance with the
usage of the eighteenth century, to designate a ground of inference
distinct from that on which we proceed in extending a law, empirical
or scientific, to a new case. But it is used in various other senses,
more or less similar, and in order to make clear the exact logical
sense, it is well to specify some of these. The original word
[Greek: analogia], as employed by Aristotle, corresponds to the word
Proportion in Arithmetic: it signified an equality of ratios, [Greek:
isotes logon]: two compared with four is analogous to four compared
with eight. There is something of the same meaning in the technical
use of the word in Physiology, where it is used to signify similarity
of function as distinguished from similarity of structure, which is
called homology: thus the tail of a whale is analogous to the tail
of a fish, inasmuch as it is similarly used for motion, but it
is homologous with the hind legs of a quadruped; a man