the economic sphere. It is always a rather foolish controversy, and I
have no intention of entering into it, but its prevalence makes it
desirable to emphasize a platitude. Economic theory must be based
upon actual fact: indeed, it must be essentially an attempt, like all
theory, to _describe_ the actual facts in proper sequence, and in true
perspective; and if it does not do this it is an imposture. Moreover,
the facts which economic theory seeks to describe are primarily
economic facts, facts, that is to say, which emerge in, and are
concerned with, the ordinary business world; and it is, therefore,
mainly upon such facts that the theory must be based. People
sometimes speak as though they supposed the economist to start from a
few psychological assumptions (e. g. that a man is actuated mainly by
his own self-interest) and to build up his theories upon such
foundations by a process of pure reasoning. When, therefore, some
advance in the study of psychology throws into apparent disrepute such
ancient maxims about human nature, these people are disposed to
conclude that the old economic theory is exploded, since its
psychological premises have been shown to be untrue. Such an attitude
involves a complete misunderstanding not merely of economics, but of
the processes of human thought. It is quite true that the various
branches of knowledge are interrelated very intimately, and that an
advance in one will often suggest a development in another. By all
means let the economist and psychologist avoid a pedantic specialism
and let each stray into the other's province whenever he thinks
fit. But the fact remains that they are primarily concerned with
different things: and that each is most to be trusted when he is upon
his own ground. When, therefore, the economist indulges in a
generalization about psychology, even when he gives it as a reason for
an economic proposition, in nine cases out of ten the economics will
not depend upon the psychology; the psychology will rather be an