Sorley opens by framing ethics as dependent on theoretical philosophy, arguing that ethical inquiry cannot be separated from metaphysical commitments. He immediately distinguishes his project from moral psychology and sociology, insisting that the fundamental question is the ethical end itself—not merely how people behave. This sharp delimitation sets the tone for a rigorous, analytical treatment.

The lectures, delivered at the University of Edinburgh in January 1884, were later revised and expanded into chapters. Sorley’s prose is dense and argumentative, marked by careful distinctions and a habit of testing definitions against their logical consequences. He engages closely with Bentham, Mill, and Spencer, but always on his own terms.

Ambiguities in Psychological Hedonism

Sorley identifies a central ambiguity in psychological hedonism: does it refer to the actual consequences of an action, its expected consequences, or its present characteristics? He argues that the theory shifts between these meanings without acknowledging the differences. For instance, if hedonism claims that people always seek pleasure, it is unclear whether this means they seek the pleasure that actually results, the pleasure they anticipate, or the pleasure inherent in the act itself. Each interpretation leads to different ethical inferences, and Sorley shows that the theory’s plausibility depends on conflating them. He further notes that the transition from psychological hedonism to ethical hedonism—the claim that one ought to seek pleasure—is not logically justified; it requires an additional premise that is rarely supplied.

Bentham’s Sanctions and Their Limits

Sorley examines Bentham’s four sanctions—physical, political, social, and religious—as motives for utilitarian conduct. He argues that Bentham’s treatment is exhaustive from his own point of view but fails to establish utilitarianism as a moral duty. The political sanction is limited by the reach of law; the social sanction is uncertain, depending on public opinion; and the internal sanction, so far as it derives from the social, is equally variable. Sorley notes that Bentham does not insist on the religious sanction as a sufficient motive, and that Paley’s reliance on it is a different approach. The upshot is that Bentham’s sanctions provide no necessary connection between individual self-interest and the greatest happiness of all.

Mill’s Proof and Its Ambiguities

Sorley turns to Mill’s logical defence of utilitarianism, focusing on the distinction of kinds of pleasure and the ambiguities in his proof. He points out that Mill’s argument that the desirable is what is desired conflates two senses of ‘desirable’: what can be desired and what ought to be desired. Sorley also criticises Mill’s appeal to the competent judge as a criterion for higher pleasures, noting that it assumes what it tries to prove—that some pleasures are intrinsically better than others. The discussion is precise and unsympathetic, revealing the logical gaps in Mill’s attempt to derive an ethical principle from psychological facts.

Evolution and the Modifiability of Pleasure

Sorley engages with Spencer’s evolutionary theory, which claims that pleasure can be attached to any activity consistent with life. He quotes Spencer’s principle that ‘a faculty to which circumstances do not allow full exercise diminishes’ and that ‘pleasure will eventually accompany every mode of action demanded by social conditions.’ Sorley acknowledges the evidence from habit and national history, but he raises a critical objection: if pleasure is indefinitely modifiable, then making pleasure the end of conduct becomes problematic, because the end itself shifts with circumstances. He argues that the doctrine of evolution, far from supporting hedonism, undermines it by showing that the content of pleasure is contingent on social conditions, not fixed by human nature.

Sorley’s lectures are best approached as a sustained argument against reducing ethics to natural facts. He does not offer a positive theory of his own, but his critical method—testing definitions, exposing ambiguities, and challenging transitions from fact to value—remains instructive. Readers interested in the logical structure of ethical naturalism will find a careful, if demanding, companion.