Skc. 8] INCOME SUMMATION 145

Interactions are essentially identical with what were discussed
 a generation ago under the title “productive services.”
 But inasmuch as the name “productive services”
is not a very happy one, and its use has been so confused and
has engendered so many verbal quibbles, it seems advisable
not to revive it. The essential fact that these “productive
services” were two-faced — negative as well as positive —
was always overlooked, and there remained no other characteristic
 which could give the phrase a definite and scientific
meaning.
Interactions constitute the great majority of the elements
which enter into income and outgo accounts. The only
services which are not merely the positive side of interactions
 are mental satisfactions — desirable conscious experiences
 — often miscalled “consumption”; and the only
disservices which are not the negative side of interactions
are pains or “labor.” But these are only the outer fringes
of the economic fabric. Between them is a connective network
 of productive processes and commercial transactions,
every fiber of which has two sides, a positive side of services
 and a negative side of disservices.

$3
The interactions between two articles or groups of articles
may, of course, consist either in causing or preventing
changes or events. The events or changes which are
caused or prevented are of three chief kinds, — changes of
form of wealth, changes of position, and changes of ownership;
 or, transformation, transportation, and transfer. We
shall take these up in order.
What is here called transformation of wealth is practically
 identical with what is usually understood by “production”
 or “productive processes.” * By the transformation
 of wealth, or the changes produced in its form, is
meant the changes of relative position of its parts. Weav-1
 Cf. Marshall, Principles of Economics, 3d ed., p. 132.

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