hat what will apply to
one will apply to all. Some logicians go so far as to say that
science cannot go any further than accurate classification.
In the words of Poincare:

The most interesting facts are those which may serve many times;
these are the facts which have a chance of coming up again. We
have been so fortunate as to have been born in a world where there
are such. Suppose that instead of sixty chemical elements there
were sixty milliards of them, that they were not some common, the
others rare, but that they were equally distributed. Then, every
time we picked up a new pebble there would be great probability of
its being formed of some unknown substance; all that we knew of
other pebbles would be worthless for it; before each new object we
should be as the new-born babe; like it we could only obey our
caprices or our needs. Biologists would be just as much at a loss if
there were only individuals and no species, and if heredity did not
make sons like their fathers.[1]

[Footnote 1: Poincare: _Foundations of Science_, p. 363.]

The aim of classification in science is grouping in such a way
as to make manifest at once similarities in the behavior of
objects. That characteristic is selected as a basis of classification
with which is correlated the greatest number of other
characteristics belonging to the facts in question. It would
be possible to classify all living things according to color, but
such a classification would be destitute of scientific value.
Biology offers some interesting examples of how an illuminating
classification may be made on the basis of a single characteristic.
It has been found, for example, that the differences
or resemblances of animals are correlated with corresponding
differences or resemblances in their teeth. In general, the
function of classification may be summarized in Huxley's
definition as modified by Jevons:

By the classification of any series of objects is meant the actual
or ideal arrangement together of those things which are like and the
separation of those things which are unlike, the purpose of the
arrangement being, primarily, to disclose the correlations or laws of
union of properties and circumstances, and, secondarily, to facilitate
the operations of the mind in clearly conceiving and retaining in
memory the characters of the object in question.

It should be noted that the object of classification is not
simply to indicate similarities but to indicate di