et
is constantly approximating them more and more nearly to a trustworthy
statement of fact. Nevertheless they are never true in that dogmatic
degree in which they seem true to the unphilosophical student of
science. Accepting as I do the validity of nearly all the general
propositions of modern science, I have constantly to bear in mind that
about them too clings the error of excessive claims to precision.

The man trained solely in science falls easily into a superstitious
attitude; he is overdone with classification. He believes in the
possibility of exact knowledge everywhere. What is not exact he declares
is not knowledge. He believes in specialists and experts in all fields.

I dispute this universal range of possible scientific precision. There
is, I allege, a not too clearly recognised order in the sciences which
forms the gist of my case against this scientific pretension. There is
a gradation in the importance of the individual instance as one passes
from mechanics and physics and chemistry through the biological
sciences to economics and sociology, a gradation whose correlations and
implications have not yet received adequate recognition, and which does
profoundly affect the method of study and research in each science.

Let me repeat in slightly altered terms some of the points raised in the
preceding sections. I have doubted and denied that there are identically
similar objective experiences; I consider all objective beings as
individual and unique. 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 Chinamen 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back to the old attitude as soon as his attention is withdrawn.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
type of error has, for instance, caught many of the race of chemists,
and ATOMS and IONS and so forth of the same species are tacitly assumed
to be similar to one another.

Be it noted that, so far as the practical results of chem