John Stuart Mill
This implication, in the first principle of the utilitarian scheme, of perfect impartiality between persons, is regarded by Mr. Herbert Spencer (in his Social Statics) as a disproof of the pretensions of utility to be a sufficient guide to right; since (he says) the principle of utility presupposes the anterior principle, that everybody has an equal right to happiness. It may be more correctly described as supposing that equal amounts of happiness are equally desirable, whether felt by the same or by different persons. This, however, is not a presupposition; not a premise needful to support the principle of utility, but the very principle itself; for what is the principle of utility, if it be not that "happiness" and "desirable" are synonymous terms? If there is any anterior principle implied, it can be no other than this, that the truths of arithmetic are applicable to the valuation of happiness, as of all other measurable quantities.
(Mr. Herbert Spencer, in a private communication on the subject of the preceding Note, objects to being considered an opponent of utilitarianism, and states that he regards happiness as the ultimate end of morality; but deems that end only partially attainable by empirical generalizations from the observed results of conduct, and completely attainable only by deducing, from the laws of life and the conditions of existence, what kinds of action necessarily tend to produce happiness, and what kinds to produce unhappiness. What the exception of the word "necessarily," I have no dissent to express from this doctrine; and (omitting that word) I am not aware that any modern advocate of utilitarianism is of a different opinion. Bentham, certainly, to whom in the Social Statics Mr. Spencer particularly referred, is, least of all writers, chargeable with unwillingness to deduce the effect of actions on happiness from the laws of human nature and the universal conditions of human life. The common charge against him is of relying too exclusively upon such deductions, and declining altogether to be bound by the generalizations from specific experience which Mr. Spencer thinks that utilitarians generally confine themselves to. My own opinion (and, as I collect, Mr. Spencer's) is, that in ethics, as in all other branches of scientific study, the consilience of the results of both these processes, each corroborating and verifying the other, is requisite to give to any general proposition the kind degree of evidence which constitutes scientific proof.)