Full Idea
What can be proved good must be so by being shown to be a means to something admitted to be good without proof. Music is good because it produces pleasure, but what proof is it possible to give that pleasure is good?
Gist of Idea
Ultimate goods such as pleasure can never be proved to be good
Source
John Stuart Mill (Utilitarianism [1861], Ch.1)
Book Reference
Mill,John Stuart: 'Utilitarianism (including On Liberty etc)', ed/tr. Warnock,Mary [Fontana 1962], p.255