 Henry Sidgwick (1838–1900), for one, read Mill as a psychological egoist (The Methods of Ethics 42–44). This is not just guilt by association. For it may appear that Mill endorses psychological egoism in his so-called “proof” of the principle of utility in Chapter IV of Utilitarianism. There, Mill aims to show that happiness is the one and only thing desirable in itself (U IV 2). To do this, he argues that happiness is desirable in itself (IV 3), and a central premise in this argument is that everyone desires his own happiness (IV 3). Mill later argues that only happiness is desirable (IV 4).