Self-interest, or rather self-love, or egoism, has been more plausibly substituted as the basis of morality. But I consider our relations with others as constituting the boundaries of morality. With ourselves, we stand on the ground of identity, not of relation, which last, requiring two subjects, excludes self-love confined to a single one. To ourselves, in strict language, we can owe no duties, obligation requiring also two parties. Self-love, therefore, is no part of morality. Indeed, it is exactly its counterpart.

Letter to Thomas Law (13 June 1814).