 Spencer’s “liberal” utilitarianism, however, differs from Mill’s in several respects, including principally the greater stringency that Spencer ascribed to moral rights. Indeed, Mill regarded this difference as the fundamental one between them. Mill responded to Spencer’s letter professing allegiance to utilitarianism, observing that he concurs fully with Spencer that utilitarianism must incorporate the “widest and most general principles” that it possibly can. However, in contrast to Spencer, Mill protests that he “cannot admit that any of these principles are necessary, or that the practical conclusions which can be drawn from them are even (absolutely) universal” (Duncan, ed., 1908:  108).[14]