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174 ECONOMIC ESSAYS IN HONOR OF JOHN BATES CLARK
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Assumptions Underlying Equation (2) Re-examined

Thus far, certainly, no reasonable critic can object. Any fundaental
 objection must be confined to questioning the truth of
he other two equations, Wy F1=W, Fs and Ws Rs=W, R,.
Ve pass on, therefore, to the second set of equations. The first
of these (Wy F1=W, F>) signifies that the two food rations are
psychologically equivalent. To be still more specific the equation
means that the psychological want-for-one-more “physical” a
of food is the same in Case 1 as in Case 2. LET
By what right can the equation W, FW. Fs 5 inferred frome
the preceding equation, S19! & me Is it, in fact, true that fo
similar families, two rations substantially equal physically are
also substantially equivalent psychologically? <I
As long as the families in Cases 1 and 2 do not materially differ
in size or character, and have substantially the same set of foods
available, though differing in price on the average by 333%,
he assumption seems at least reasonable. If, to go back to
‘physical” sameness, there be similar food articles, similar hoard
ng-houses, hotels, cafés, etc., in both countries, differing merely
in that the price of a given ration in Oddland is 3315% higher
han the corresponding grade in Evenland, we have in each country
 a series of food opportunities distinguishable as, say, first
class, second class, third class, etc., as on an ocean steamer, except
that in the present instance the scale of gradations steps up continuously
 by infinitesimal intervals instead of in big jumps. Each
family merely has to choose its place on this scale. It is still
possible, despite the fact that quality varies as well as quantity,
o speak of a physical food unit or a physical unit of house accommodation
 or clothing. To be specific, let us suppose a list of
food rations in Evenland, A, B, C, D, such that B costs $1 more
than A, C likewise $1 more than B, D $1 more than C and so on,
and such as average families of the same size and general character
 would choose according to their purse, the very poorest
families choosing A and the very richest families choosing Z.
The difference in the food as between A and B, or between B and
, or any other one step-up each costing one dollar more than its
predecessor in the scale, may be called one “food-unit” and this
difference may henceforth be thought of i one “pound.”