Amartya K. Sen, "Impossibility of Paretian Liberal," より抜粋。
Ⅲ. An Example
We give now a simple example of the type of impossibility that is involved
in Theorem Ⅱ by taking a special case of two individuals and three
alternatives. There is one copy of a certain book, say Lady Chatterly's
Lover, which is viewed differently by 1 and 2. The three alternatives are:
that individual 1 reads it (x), that individual 2 reads it (y),and that no
one reads it (z). Person 1, who is a prude, prefers most that no one reads
it, but given the choice between either of the two reading it, he would
prefer that he read it himself rather than exposing gullible Mr.2 to the
influences of Lawrence. (Prudes, I am told, tend to prefer to be censors
rather than being censored.) In decreasing order of preference, his ranking
is z, x, y. Person 2, however, prefers that either of them should read it
rather than neither. Furthermore, he takes delight in the thought that
prudish Mr. 1 may have to read Lawrence, and his first preference is that
person 1 should read it, next best that he himself should read it, and
worst that neither should. His ranking is, therefore, x, y, z..
Now if the choice is precisely between the pair (x, z), i.e., between
person 1 reading the book and no one reading it, someone with liberal
values may argue that it is person 1's preference that should count; since
the prude would not like to read it, he should not be forced to. Thus, the
society should prefer z to x. Similarly, in the choice exactly between
person 2 reading the book (y) and no one reading it (z), liberal values
require that person 2's preference should be decisive, and since he is
clearly anxious to read the book he should be permitted to do this. Hence y
should be judged socially better than z. Thus, in terms of liberal values
it is better that no one reads it rather than person 1 being forced to read
it, and it is still better that person 2 is permitted to read the book
rather than no one reading it. That is, the society should prefer y to z,
and z to x. This discourse could end happily with the book being handed
over to person 2 but for the fact that it is a Pareto inferior alternative,
being worse than person 1 reading it, in the view of both persons, i.e., x
is Pareto superior to y.
Every solution that we can think of is bettered by some other solution,
given the Pareto principle and the principle of liberalism, and we seem to
have an inconsistency of choice.
※ 東京大学の学生のみなさんへ
Choice, Welfare and Measurement は、総開架 S600:2126, もしくは 経図
1:1911 にあります。
その部分訳の、大庭健、川本隆史訳『合理的な愚か者：経済学＝倫理学的探求』（勁草書房、1989）は、養図開架
331:449, 養養図第三 331.15:Se, 経図 83:1293 などにあります。