d
therefore no argument from indirect evidence. Huxley sets forth this
fundamental truth clearly and impressively at the beginning of the first
of his "Lectures on Evolution" (see p. 234).

For practical purposes the various types of this inference from
similarity can be conveniently thrown into three groups. As will be
obvious, there is no fixed and impassable line between them.

"If an inference relies upon a resemblance that is newly seen, rare, or
doubtful, it is called an inference from analogy; if it is made upon the
basis of an established classification, it is called a generalization;
if it involves a variety of resemblances so combined as to bear upon a
single point, it is usually or frequently called an inference from
circumstantial evidence."[25]

I will take up each of these types and show how we use them in the
practical work of argument. It will be seen that they vary greatly in
certainty of results.

34. Reasoning from Analogy. Analogy in its most tenuous form is
weak as a basis for an actual inference, though it is often effective as
a means of expressing an intuitive judgment where the reasons are too
subtle and diffused for formal explanation. When Lincoln in the middle
of the Civil War said that men do not swap horses while they are
crossing a stream, the analog, though subtle, was felt to be real.
Popular adages and proverbs are common modes of expressing such
deep-lying analogies: for example, "Where there is smoke there is fire";
"The slothful man saith, There is a lion in the way." Poetry too is full
of these subtle, pregnant similarities which link things in some one
aspect, but fail for all others.

To die; to sleep;
No more; and by a sleep to say we end
The heart-ache and the thousand natural shocks
That flesh is heir to. 'Tis a consummation
Devoutly to be wish'd. To die; to sleep;--
To sleep? Perchance to dream! Ay, there's the rub;
For in that sleep of death what dreams may come,
When we have shuffl'd off this mortal coil,
Must give us pause.

But, as in this case of Hamlet's, poetical analogies will not bear much
strain; the aspect in which the similarity holds is usually the only
aspect the two cases have in common, and to take poetry as a precise
formulation of fact is to sin against both humor and sound reasoning.

In daily life we are constantly reasoning by analogy. If you argue that
a certain man who has been successf