attributing to a
body in consequence of some of its properties, all those other
properties in virtue of which it is referred to a particular class, is
an act of inference. And, on the other hand, the forming of a
generalisation is the putting together in one class all those cases
which present like relations; while the drawing a deduction is
essentially the perception that a particular case belongs to a certain
class of cases previously generalised. So that as classification is a
grouping together of _like things_; reasoning is a grouping together of
_like relations_ among things. Add to which, that while the perfection
gradually achieved in classification consists in the formation of groups
of _objects_ which are _completely alike_; the perfection gradually
achieved in reasoning consists in the formation of groups of _cases_
which are _completely alike_.

Once more we may contemplate this dominant idea of likeness as exhibited
in art. All art, civilised as well as savage, consists almost wholly in
the making of objects _like_ other objects; either as found in Nature,
or as produced by previous art. If we trace back the varied art-products
now existing, we find that at each stage the divergence from previous
patterns is but small when compared with the agreement; and in the
earliest art the persistency of imitation is yet more conspicuous. The
old forms and ornaments and symbols were held sacred, and perpetually
copied. Indeed, the strong imitative tendency notoriously displayed by
the lowest human races, ensures among them a constant reproducing of
likeness of things, forms, signs, sounds, actions, and whatever else is
imitable; and we may even suspect that this aboriginal peculiarity is in
some way connected with the culture and development of this general
conception, which we have found so deep and widespread in its
applications.

And now let us go on to consider how, by a further unfolding of this
same fundamental notion, there is a gradual formation of the first germs
of science. This idea of likeness which underlies classification,
nomenclature, language spoken and written, reasoning, and art; and which
plays so important a part because all acts of intelligence are made
possible only by distinguishing among surrounding things, or grouping
them into like and unlike;--this idea we shall find to be the one of
which science is the especial product. Already during the stage we have
been describing, there has existed