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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 funda- 
ental 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 coun- 
try 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 con- 
tinuously 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 accom- 
modation 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 char- 
acter 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.”