of Edinburgh, Session 1883 - 84 . 
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units of potential energy as combustible (physical value) ; (3) that 
the former is capable of maintaining an average adult for a definite 
time, while the latter possesses a definite power of sensory stimulus 
(physiological value) ; (4) that corresponding to the preceding 
physiological functions are their subjective aspect, known as wants 
or desires (psychological value) ; (5) that, as property’-, they acquire 
a sociological “value,” which cannot as yet be entered upon. 
The idealistic position, though extremely popular, has never been 
consistently maintained ; the reverse position is often tacitly taken, 
as apparently in the dogma that “labour is a commodity,” and the 
like. 
The attempt then to base the psychology of economics upon the^ 
aspects of value, and much more to make it the centre of the 
whole science, turns out futile ; so far from being fundamental, it is 
in fact almost superfluous, since it is either the subjective expression 
of an actual objective value (physical, biological, or sociological), or 
an erroneous hypothetical estimate of one or more of these. 
§40. Wants and Desires . — Can “wants and desires,” however,, 
be taken as completely expressing the psychology of action ? Pro- 
bably not completely, since there is much ground for suspecting 
that complex associations never formulated in consciousness play an 
important part ; perhaps, too, that even lower states of cerebral 
activity have their share in determining action. 
Let us see, however, how the conception is developed by econo- 
mists. Their current positions may most fairly be stated by quota- 
tions from well-known authors. “ Political economy teaches the 
relation of man to those objects of his desire which he can obtain 
only by his efforts ” (Walker, Science of Wealth, p. 2). “ The 
objects or satisfactions obtained by these efforts are collectively 
called wealth.” Again, “ wealth is whatever satisfies a desire or 
serves a purpose.” Again, according to J. B. Say, “that society is 
most civilised which produces most and consumes most;” or, in 
other words, which has the greatest quantity of artificial wants. 
From the preceding it follows — (1) that all wants and desires are 
equally valid in the eyes of the economist, who can make no other 
criticism of wealth ; (2) that the only recognisable progress lies in 
differentiation, and in this most economists fully concur. 
Despite the importance attached to wants and desires, they have 
