Section 27. (e) Analogy.
Analogy is the least negligible of all methods of induction because
it rests at bottom on the postulate that one thing which has a number
of qualities in common with another will agree with that other in
one or more additional qualities. In cases of
analogy, identity is
never asserted; indeed, it is excluded, while a certain parallelism
and agreement in specific points are assumed, i. e., introduced tacitly
as a mutatis mutandis. Consider Lipps's examples. He calls
analogy the transfer of judgment or the transition from similar to
similar, and he adds that the value of such a process is very variable.
If I have perceived x times that flowers of a certain color have perfume,
I am inclined to expect perfume from flowers of the same
color in x+1 cases. If I have observed x times that clouds of a
certain structure are followed by rain I shall expect rain in the
x+1st case. The first analogy is worthless because there is no
relation between color and perfume; the second is of great value
because such a relation does exist between rain and clouds.
Simply stated, the difference between these two examples does
not consist in the existence of a relationship in the one case and
the absence of a relationship in the other; it consists in the fact
that in the case of the flowers the relationship occurs now and then
but is not permanently knowable. It is possible that there is a
natural law controlling the relation between color and odor, and if
that law were known there would be no question of accident or of
analogy, but of law. Our ignorance of such a law, in spite of the
multiplicity of instances, lies in the fact that we are concerned only
with the converse relationships and not with the common cause of
perfume and color. Suppose I see on the street a large number of
people with winter over-coats and a large number of people with
skates in their hands, I would hardly ask whether the coats are
conditioned or brought out by the skates or the skates by the coats.
If I do not conclude that the cold weather is the condition both of
the need of over-coats and the utility of skates, I will suppose that
there is some unintelligible reflexive relation between over-coats
and skates. If I observe that on a certain day every week there
regularly appear many well-dressed people and no workingmen on
the street, if I am ignorant of the fact that Sunday is the cause
of the appearance of the one and the disappearance of the other, I
shall try in vain to find out how it happens that the working people
are crowded out by the well-dressed ones or conversely.
The danger of analogy lies in the fact that we prefer naturally
to depend on something already known, and that the preference is
the greater in proportion to our feeling of the strangeness and
ominousness of the particular intellectual or natural regions in
which we find ourselves. I have already once
demonstrated[1] how
disquieting it is to notice, during the examination of the jury, that
the jurymen who ask questions try to find some relation to their
own trades even though this requires great effort, and seek to bring
the case they are asking about under the light of their particular
profession. So, however irrelevant the statement of a witness may
be, the merchant juryman will use it to explain Saldo-Conti, the
carpenter juryman to explain carpentry, the agriculturist to notice
the farming of cattle, and then having set the problem in his own
field construct the most daring analogies, for use in determining the
guilt of the accused. And we lawyers are no better. The more
difficult and newer a case is the more are we inclined to seek analogies.
We want supports, for we do not find firm natural laws, and
in our fear we reach out after analogies, not of course in law, because
that is not permitted, but certainly in matters of fact. Witness X
has given difficult testimony in a certain case. We seek an analogy
in witness Y of an older case, and we observe the present issue
thus analogically, without the least justification. We have never
yet seen drops of blood on colored carpets, yet we believe in applying
our experience of blood stains on clothes and boots analogically.
We have before us a perfectly novel deed rising from perverted
sexual impulse—and we presuppose that the accused is to be
treated altogether analogously to another in a different case,
although indeed the whole event was different.
Moreover the procedure, where the analogy is justified, is complex.
"With insight," says Trendelenburg, "did the ancients regard
analogy as important. The power of analogy lies in the construction
and induction of a general term which binds the subconcept with
regard to which a conclusion is desired, together with the individual
object which is compared with the first, and which is to appear as
a mediating concept but can not. This new general term is not,
however, the highest concept among the three termini of the conclusion;
it is the middle one and is nothing else than the terminus
medius of the first figure." This clear statement shows not only
how circumstantial every conclusion from analogy is, but also how
little it achieves. There is hardly any doubt of the well-known
fact that science has much to thank analogy for, since analogy is
the simplest and easiest means for progress in thought. If anything
is established in any one direction but progress is desired in another,
then the attempt is made to adapt what is known to the proximate
unknown and to draw the possible inference by analogy. Thousands
upon thousands of analogies have been attempted and have failed,—
but no matter; one successful one became a hypothesis and finally
an important natural law. In our work, however, the case is altogether
different, for we are not concerned with the construction of
hypotheses, we are concerned with the discovering of truth, or with
the recognition that it cannot be discovered.
The only place where our problems permit of the use of analogy
is in the making of so-called constructions, i. e., when we aim to
clarify or to begin the explanation of a case which is at present
unintelligible, by making some assumption. The construction then
proceeds in analogy to some already well known earlier case. We
say: "Suppose the case to have been so and so," and then we begin
to test the assumption by applying it to the material before us,
eliminating and constructing progressively until we get a consistent
result. There is no doubt that success is frequently attained in this
way and that it is often the only way in which a work may be begun.
At the same time, it must be recognized how dangerous this is,
for in the eagerness of the work it is easy to forget that so far, one
is working only according to analogy by means of an assumption
still to be proved. This assumption is in such cases suddenly
considered as something already proved and is counted as
such with the consequence that the result must be false. If you add
the variability in value of analogy, a variability not often immediately
recognized, the case becomes still worse. We have never
been on the moon, have therefore apparently no right to judge the
conditions there—and still we know—only by way of analogy—
that if we jumped into the air there we should fall back to the
ground. But still further: we conclude again, by analogy, that
there are intelligent beings on Mars; if, however, we were to say
how these people might look, whether like us or like cubes or like
threads, whether they are as large as bees or ten elephants, we
should have to give up because we have not the slightest basis for
analogy.
In the last analysis, analogy depends upon the recurrence of
similar conditions. Therefore we tacitly assume when we judge
by analogy that the similarity of conditions contains an equivalence
of ultimately valid circumstance. The certainty of analogy is as
great as the certainty of this postulate, and its right as great as the
right of this postulate.
If, then, the postulate is little certain, we have gained nothing
and reach out into the dark; if its certainty is great we no longer
have an analogy, we have a natural law. Hence, Whately uses the
term analogy as an expression for the similarity of relation, and in
this regard the use of analogy for our real work has no special significance.
Concerning so-called false analogies and their importance
cf. J. Schiel's Die Methode der induktiven Forschung (Braunschweig
1868).
[[1]]
Manual for Examining Justices.