 In both passages Mill makes what is now a familiar diagnosis of the troubles with psychological egoism. He thinks that psychological egoism is ambiguous between a true but trivial thesis about the ownership of desire—an agent necessarily acts on his own desires—and a substantive but wildly implausible thesis about the content of desires—an agent’s ultimate desire is always and necessarily to promote his own interests or pleasure. If so, there is no thesis that is both substantive and plausible. The substantive thesis may seem speciously attractive if we tacitly confuse it with the trivially true thesis. But it seems clear from Bentham’s and James Mill’s worries about the conflict between ruler’s interests and the interest of the ruled that they intend something like the substantive psychological thesis. But if they do so because they conflate it with the trivial but true thesis, then they commit the fallacy of equivocation.