available. More can be said with reasonable generality
about magnitudes such as the ratio of money holdings to
transactions for the public as a whole and for certain
sections of the public, or the ratio of consumption ex-
penditures to national income, than about relationships
between certain measurable quantities on the one hand,
and wages or prices in specific industries on the other. The
relationships that are significant for value theory cannot
be read from aggregative national balance sheets or from
overall banking statistics. They can be derived only from
intensive study of individual market behavior or the mar-
ket behavior of comparatively narrow groups.

This, of course, follows from the definitions of the fields
here considered. Value theory is concerned with relative
prices, that is, with relationships between specific prices;
the general price level, which is a broad aggregative con-
cept, is defined to be a problem of monetary theory.
Similarly, the output produced and the employment
supplied by individual firms and industries are determined
by precisely the same factors which determine individual
prices, that is to say, the output and employment of
specific firms and industries are problems of value theory.
Aggregate output and employment are problems of the
other type of theory, which by now has reached a more
advanced stage of development. It follows almost directly
from the definitions of these various fields that the diffi-
culties standing in the way of collecting relevant material
and of arriving at reasonably useful generalizations are
greater for the one type of inquiry than for the other.
For one of the two types of inquiry (monetary theory and
the theory of employment) is mainly concerned with over-
all data and overall relationships, while the other (value
theory) is, by definition, concerned with specific data and

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