hysiologist leaves
out of account.[28]

The question of the validity of an analogy in reasoning is always, as
here, whether the similarity on which the reasoning rests really runs
between the two cases in hand, or is not merely a general resemblance
expressed by some phrase or word which seems to mean more than it does.
In other words, when you are testing an analogy, whether your own or an
opponent's, make sure that the similarity is real for the present case.
A picturesque figure of speech may add life to an argument, but it may
also cover a gap in the reasoning.

36. Reasoning by Classification or Generalization. Obviously the
strength of reasoning from analogy increases with the number of cases
which you can point to as showing the similarity on which you rely, for
you can then begin to generalize and classify.

Analogy expresses our natural tendency to assimilate the new to the old,
to interpret what is strange and unfamiliar in the light of what we
already know. It may therefore be described as classification in the
making. The resemblances which guide us are called analogies so long as
they are newly seen, rare, or doubtful; but as the number of cases
increases, analogy passes by insensible stages into established
classification.[29]

An excellent example of this transition may be seen in the present state
of the argument in favor of commission government: at first, as we have
seen, it depended chiefly on reasoning from analogy; by this time enough
cities have adopted the plan to make it possible to classify them, and
so reason by generalization.

Generalization and classification, it may be noted in passing, are two
aspects of the same process of thought. When one passes from the
individual facts to the larger fact which brings them together, as in
the assertion, _Members of the Phi Beta Kappa are good scholars_, one
makes a generalization; when one asserts of an individual the larger
fact, as in the assertion, My _brother is a good scholar_ (My _brother
belongs to the class Good Scholars_), one makes a classification.

When a classification or generalization is constant and familiar, it
brings forth, by the natural economy of language, a name for the class
or the principle; "federation," "deciduous trees," "emotion," "terminal
moraine," are all names of classes; "attraction of gravity," "erosion,"
"degeneration," "natural selection," are names of principles which sum
up acts of generalization. Almost alw