Pleasure is the only thing desired; therefore pleasure is the only thing desirable.
 Bertrand Russell, A History of Western Philosophy (1945). copy citation

Context

“There was in his day not much material for forming a judgement as to the working of democratic institutions, and his optimism was therefore perhaps excusable, but in our more disillusioned age it seems somewhat naïve. John Stuart Mill, in his Utilitarianism, offers an argument which is so fallacious that it is hard to understand how he can have thought it valid. He says: Pleasure is the only thing desired; therefore pleasure is the only thing desirable. He argues that the only things visible are things seen, the only things audible are things heard, and similarly the only things desirable are things desired. He does not notice that a thing is “visible”” source