they have put together the
formulae which would be useful if they had the data; and, in short, that
you can get more out of a mill than you put into it; or, in other words,
that more conclusions than really follow can be got out of premisses,
simply because you show what would follow if you had the required
knowledge. When the attempt is made, as it seems to me to be made
sometimes, to deduce economical laws from some law of human desire--as
from the simple theorem that equal increments of a commodity imply
diminishing amounts of utility--I should reply not only that the
numerical data are vaguely defined and incapable of being accurately
stated, but that the attempt must be illusory because the conclusions
are not determinable from the premisses. The economic laws do not follow
from any simple rule about human desires, because they vary according to
the varying constitution of human society; and any conclusion which you
could obtain would be necessarily confined to the abstract man of whom
the law is supposed to hold good. Every such method, therefore, if it
could be successful, could only lead to conclusions about human desire
in general, and could throw no light upon the special problems of
political economy, which essentially depend upon varying industrial
organisation.

I will not, however, go further. You must either, I hold, limit
Political Economy to the field of statistical inquiry, or admit that,
as a part of sociology, it deals with questions altogether beyond the
reach of mathematics. Like physiology, it is concerned with results
capable of numerical statement. The number of beats of the pulse, or
the number of degrees of temperature of the body, are important data in
physiological problems. They may be counted, and may give rise to
mathematically expressible formulae. But the fact does not excuse us
from considering the physical conditions of the organs which are in
some way correlated with these observed phenomena; and, in the case of
Political Economy, we have to do with the social structure, which is
dependent upon forces altogether incapable of precise numerical
estimates. That, at least, is my view; and I shall apply it to
illustrate one remark, which must, I think, have often occurred to us.
Political Economy, that is, often appears to have a negative rather
than a positive value. It is exceedingly potent--so, at least, I
think--in dispersing certain popular fallacies; but it fails when we
regard it