An Enquiry Concerning the Principles of Morals

Hume's recasting of the moral theory of Book 3 of his Treatise as a shorter, more polished enquiry, which he himself thought his best book. Its method is empirical: collect the qualities people everywhere praise or blame, and find what they share. The answer is that personal merit consists in qualities useful or agreeable to the person or to others. Hume starts with benevolence, then argues that public utility is the sole origin of justice, which is why rules of property lapse in extreme scarcity or plenty. Later sections cover qualities useful to ourselves, such as prudence and industry, and qualities immediately agreeable, such as wit, good manners and cheerfulness. Celibacy, fasting, humility and the other 'monkish virtues' are rejected because they serve no one. The Conclusion faces the 'sensible knave' who keeps the rules only when it pays. Appendix I argues that reason informs us of the facts, but sentiment makes the moral judgement.

It is the most readable statement of sentimentalist ethics and a direct ancestor of utilitarianism, written by a philosopher with a sharp eye for how people actually praise and blame.