152 ECONOMIC ESSAYS IN HONOR OF JOHN BATES CLARK
with the unfortunate result that his unified conception is converted
 into the dualistic conception already foreshadowed by
Hadley. This is the passage: *

Capital is a fund and income a flow. This difference between capital
and income is, however, not the only one. There is another important
difference, namely, that capital is wealth, and income is the service
of wealth. We have, therefore, the following definitions: A stock of
wealth existing at an wnstant of time is called capital. A flow of
services through a period of time is called income.

Now it must be said of these dualistic definitions that they are
quite useless for the purpose in view. Fisher's own work on
capital and income deals mainly with financial conceptions
untouched in these definitions, incomes as price-quanta, discounted
 and summed up in capital (also a price quantum) conceived
 of as the present worth of claims to future monetary
incomes, no matter whence or how derived (even from intangible
rights). And the definitions are at least in part tautological,
for while it would be logically possible (even though theoretically
useless) to have a fund of wealth (material goods) and to contrast
 it with a flow of the same goods, it is not possible to conceive
 of a literal stock of services at an instant of time; it is
possible only to conceive of their present worth as a financial
fund at an instant of time. Services (taken in the sense of uses
either of wealth or of human beings) may conceivably be delayed
or hastened, but they are in their very nature a flow; they cannot
be heaped up and constitute a stock of services. They can at
most, as they occur, be “incorporated” in durable forms of wealth.
If this is so, then why this elaborate contrast between a flow of
services and a fund of something quite different? It is the
vestigial remains of the older conception that Fisher has been
obliged to discard.
The idea of a “fund” as a financial sum, estimate, or valuation,
at an instant of time, has become confused with the idea of a
“fund” as a heap or store of physical goods existing at an instant
of time. The phrases of Fisher's definitions form a superficial,
verbal bond of connection between the old conception and the new
one, while in fact the essential distinction has become that not
between income as a flow and capital as a fund (of the “very
same” material things) but that between a valuation of services
L The Nature of Capital and Income (1906), p. 52. Italics in the original.