Mill’s sex life is important in terms of understanding him as a man, of course, but there are some philosophical implications too. Mill was his century’s pre-eminent thinker on the content of a good life—of which sex must surely form a part. More specifically, in his version of utilitarianism, Mill insisted that it was not only the quantity of pleasure that counted but its intrinsic quality. He distinguished between lower pleasures, defined as ‘animal appetites’ consisting of ‘mere sensation’ and ‘higher’ pleasures ‘of the intellect, of the feelings and imagination, and of the moral sentiments’. Mill suggested sampling, to see which was preferable: ‘Of two pleasures, if there be one to which all or almost all who have experience of both give a decided preference, irrespective of any feeling of moral obligation to prefer it, that is the more desirable pleasure.’ Mill’s view was that the majority of people who had experienced the pleasure of, say, having sex and reading poetry, would find the latter a more intrinsically valuable pleasure; but according to his own philosophical rules he would have been prohibited form making any such judgement unless he had himself experienced both.

Richard Reeves, John Stuart Mill: Victorian Firebrand, London, 2007, p. 154