 By showing that happiness is desirable, that nothing other than happiness is desirable, and that every person’s happiness is equally desirable, Mill holds that “the principle of utility is proved” (Utilitarianism, X: 239). It is not, of course, a proof in the traditional sense of being a logical deduction of the principle of utility. Indeed, Mill acknowledges that in a strict sense, “ultimate ends are not amenable to direct proof” (Utilitarianism, X: 207; cf. X: 234). Being based on critical examination of how we do reason, claims about how we ought to reason—whether practically or theoretically—must remain provisional, and open to ongoing correction by further observations of our reasoning practices. Nevertheless, Mill holds, the ‘proof’ presents “[c]onsiderations […] capable of determining the intellect” (Utilitarianism, X: 208). As such, the principle of utility—“the doctrine that all things are good or evil, by virtue solely of the pleasure or the pain which they produce”—is shown to have “rational grounds” (The Protagoras, XI: 61; Utilitarianism, X: 208).