G. E. Moore’s Principia Ethica defended the view that “good” names a simple, non-natural property that cannot be reduced to natural facts (such as pleasure). This reinforced a broadly intuitionist picture in which some moral truths are known directly. Even when later philosophers rejected Moore’s conclusions, they often worked within the problems he sharpened.
H. A. Prichard argued that much moral philosophy makes a basic mistake: trying to prove what we ought to do from non-moral premises. He claimed that ordinary moral obligations (like keeping promises) are grasped directly, not derived by argument. This helped set a 20th-century intuitionist agenda focused on immediate knowledge of duty.
W. D. Ross’s The Right and the Good presented a pluralist form of deontology: we have multiple basic duties (e.g., fidelity, gratitude, justice) that can conflict. Ross called these duties prima facie—meaning they normally count in favor of an action, but can be overridden by stronger duties in particular situations. This became a central reference point for mid-century intuitionism.
C. D. Broad’s Five Types of Ethical Theory offered an influential analytic survey of major ethical approaches. While not limited to intuitionism, it helped establish the style of careful, comparative ethical theorizing common in British and American philosophy classrooms. The book also provided a framework for discussing why intuitionist approaches seemed attractive—or problematic—compared with rivals.
A. J. Ayer’s Language, Truth, and Logic argued that many traditional philosophical claims fail a verificationist test of meaning. In ethics, Ayer advanced emotivism, treating moral judgments as expressions of attitude rather than statements of fact. This directly threatened intuitionist views that moral judgments can be true or false and known by intuition.
In Foundations of Ethics (based on his 1935–36 Gifford Lectures), Ross expanded and refined his ethical system, including how we think about value and the structure of moral reasoning. This work helped consolidate “Rossian” intuitionism as a comprehensive approach rather than only a list of duties. It also gave later critics a clearer target when challenging intuitionist epistemology.
A. C. Ewing argued that ethical thought involves more than empirical reporting or emotional expression. In Reason and Intuition, he defended the role of rational insight in ethics and related areas of philosophy. This book signaled a continuing British intuitionist line during a period when logical positivism was influential.
C. L. Stevenson’s Ethics and Language gave emotivism a more sophisticated and influential form than earlier presentations. It analyzed how ethical language works in disagreement, persuasion, and deliberation. For intuitionists, Stevenson sharpened the challenge: if moral language is mainly action-guiding and persuasive, what kind of “knowledge” could moral intuition provide?
In The Definition of Good, Ewing defended an intuitionist-friendly view of ethics that treated knowledge of good and duty as possible without reducing moral terms to non-moral ones. The book provided a mid-century attempt to keep non-naturalist and deontological ideas viable amid increasing interest in language-focused metaethics. It also helped carry British intuitionist concerns into postwar debates.
Prichard’s Moral Obligation collected essays and lectures (some published earlier and some from his papers) into a single volume after his death. The collection reinforced his core claim that obligation is not derived from theories about the good or from self-interest. It also helped maintain Oxford-style intuitionism as a living option for mid-century readers.
R. M. Hare’s The Language of Morals agreed that moral judgments are not straightforward descriptions, but he argued they function as prescriptions (guiding action) that must be universalizable (applied consistently across similar cases). This shifted attention from intuition as “moral perception” to logical constraints on moral speech and reasoning. The result further pressured intuitionists to explain how intuition fits with the practical and linguistic roles of moral judgment.
By the late 1950s and around 1960, British and American ethics increasingly focused on analysis of moral language (emotivism and prescriptivism) and on new methods for justifying principles. Ross, Prichard, and Ewing still anchored a major intuitionist alternative, especially through the idea of plural, prima facie duties and the claim that some moral truths are self-evident. But the leading questions had shifted toward how moral discourse works and how competing moral judgments can be rationally settled.
20th‑century moral intuitionism in British and American ethics (1910–1960)