http://mises.org/journals/qjae/pdf/qjae6_1_3.pdf
That is the crux of the matter. Neoclassical economists act as if they can
have both cardinal and ordinal rankings at the same time and in the same
respect. That is, they say that because they can order bundles on the basis of
the cardinal number assigned to it by a specific function, the order so generated
is a rank-order, and that the utilities being so considered are ordinal. This
is incorrect. Were it truly an ordinal ranking, it would not be absolutely necessary
to use the cardinal numbers from which the ranking was generated in
their mathematical calculations. Rather, the ordinal numbers corresponding
to the ranking generated from the cardinal numbers could themselves be usedin such calculations.
Therefore, the order generated by neoclassical utility
functions is not a rank ordering in any meaningful sense of the word.
Furthermore, neoclassical economists properly maintain that the ranking
of a set of bundles generated by one of their utility functions is invariant
under a monotonic transformation thereof.16 That is, although one bundle of
goods from a set of bundles might be assigned the number 100 by one function,
F, and the number 10,000 by another function, F2 (a monotonic transformation
of F), in either case the bundle would have the same ranking within
the set of bundles. Therefore, in order to know the rank of a basket of goods,
all one needs to know is its assigned number, and the numbers assigned to
other bundles. Note well that all that is necessary to know in order to assign
the appropriate number to each and every specific bundle is its own specific
contents. No knowledge whatsoever of the contents of any other bundle or
bundles is necessary.17 Therefore, baskets of goods may be ranked without
any comparison with the contents of other bundles. Most assuredly, such a
ranking does not qualify as ordinal in nature.
…
Put another way, let there be two (2) bundles, A and B, to which a neoclassical
utility function assigns the cardinal numbers 20 and 30, and ordinal
numbers (necessarily based thereon) 2nd and 1st, respectively. If a third bundle,
C, is now to be ranked, all that is necessary to know are the elements of
bundle C and the concomitant cardinal number assigned to it by the utility
function. Thus, if the utility function, operating on the elements of C, yields
the cardinal number 25 for C, then the ordinal ranking becomes: B is 1st, C
is 2nd, and A is 3rd. If, however, the utility function were a “true” ordinal utility
function, in order to rank C, we would need to know more than that the
ordinal numbers assigned to A and B are 2nd and 1st, respectively, and the elements
of C. We would need to know the elements A and of B, as well.
…
that results from using cardinal utility functions.
Furthermore, neoclassicists make use of indifference curve analysis
and the marginal rate of substitution (MRS) to analyze consumer choice.
The MRS in the two-good case is defined as: dy/dx(dU = 0) = -Ux/Uy.27 Therefore,
using either U1 or U2 as the utility function, dy/dx = -y/x. However,
utility maximization requires that the MRS be equal to the negative of the
ratio of the price of x to that of y (-px/py). Therefore for either bundle A or
C to be optimal the prices of x and y must be the same and, therefore, the
MRS = -y/x = -100/100 = -1, whereas for B or D to be optimal the price
ratios of x to y must be -100/121 or -400/420.25, respectively and, therefore,
the MRS = -y/x = -100/121 or -400/420.25, respectively. But -1, -
100/121, and -400/420.25 are cardinal numbers, not ordinal numbers. It is
difficult to see how this can be denied. Consequently, one reason that neoclassicists
are in error is precisely because, de facto, they switch from
ordinal to cardinal utility when their utility functions generate cardinal
numbers and they use these cardinal numbers in their calculations.
…
SUMMARY AND CONCLUSION
In sum, the cardinal utility numbers generated by neoclassical utility functions
provide more information than do their ordinal counterparts. In fact,
for any given set of bundles they contain all of the information implicit in
ordinal utility numbers for the same set, plus they provide additional information
concerning the intensity of the preference for any one bundle relative to any other. It is precisely because utility functions cannot be used to calculate
ordinal rankings of bundles without prior calculation of their cardinal
utility numbers that the use of utility functions is unacceptable for economic
purposes. Moreover, although meaningless with respect to the reality of actual
individuals’ preferences, this extra information is harmful because it is misleading.
I conclude by reiterating the purpose of this article. I have attempted to
demonstrate that neoclassical utility functions are an invalid means of analyzing
consumer behavior for three reasons: first, and most important,
because such functions, and their attendant rankings, are cardinal, not ordinal
in nature; second, because, with respect to the set of bundles relevant to
actual human beings, such functions are not continuous and, therefore, not
differentiable; and, third, because such functions do not correctly, consistently,
and properly include dimensions/units.
Let me put this in another way. I will accept the validity of utility functions
as soon as its proponents can show me how to perform basic mathematical
or arithmetic operations on such ordinal numbers as 1st, 3rd, 6th, and
17th.