Everybody knows that the same sum of money is of much greater value to a poor man that to a rich one. Give £10 a year to the man who has but £10 a year, you double his income, and you nearly double his enjoyments. Add £10 more, you do not add to his enjoyments so much as you did by the first £10. The third £10 is less valuable than the second, and the fourth less valuable than the third. To the possessor of £1,000 a year the addition of £10 would be scarcely perceptible; to the possessor of £10,000 it would not be worth slooping for.

The richer a man is the less he is benefited by any further addition to his income. The man of £4,000 a year has four times the income of the man who has but £1,000; but does anybody suppose that he has four times the happiness?

John Stuart Mill, Journals and Debating Speeches, in Francis E. Mineka (ed.) Collected Works of John Stuart Mill, Toronto, 1963, p. 336