sciences to which I wish to call your attention, and which forms the
gist of my case against this scientific pretension. There is a gradation
in the importance of the instance as one passes from mechanics and
physics and chemistry through the biological sciences to economics and
sociology, a gradation whose correlatives and implications have not yet
received adequate recognition, and which do profoundly affect the method
of study and research in each science.

Let me begin by pointing out that, in the more modern conceptions of
logic, it is recognised that there are no identically similar objective
experiences; the disposition is to conceive all real objective being as
individual and unique. This is not a singular eccentric idea of mine; it
is one for which ample support is to be found in the writings of
absolutely respectable contemporaries, who are quite untainted by
association with fiction. It is now understood that conceivably only in
the subjective world, and in theory and the imagination, do we deal with
identically similar units, and with absolutely commensurable quantities.
In the real world it is reasonable to suppose we deal at most with
_practically_ similar units and _practically_ commensurable quantities.
But there is a strong bias, a sort of labour-saving bias in the normal
human mind to ignore this, and not only to speak but to think of a
thousand bricks or a thousand sheep or a thousand sociologists as though
they were all absolutely true to sample. If it is brought before a
thinker for a moment that in any special case this is not so, he slips
back to the old attitude as soon as his attention is withdrawn. This
source of error has, for instance, caught nearly the whole race of
chemists, with one or two distinguished exceptions, and _atoms_ and
_ions_ and so forth of the same species are tacitly assumed to be
similar one to another. Be it noted that, so far as the practical
results of chemistry and physics go, it scarcely matters which