The British philosopher Henry Sidgwick (1838–1900) has had a major influence on Rawls, especially on his methodology. “The Methods of Ethics is, I believe, the outstanding achievement in modern moral theory…the first truly academic work in moral theory, modern in both the method and spirit” (CP 341). In LHPP, Rawls dedicates four lectures to Sidgwick and he also wrote a “Foreword” for Methods of Ethics when it was last republished (1981, v–vi).

Rawls has borrowed heavily from Sidgwick’s notion of the methods of ethics. “Sidgwick assumes that a rational method is one that can be applied to all rational (and reasonable) human beings to get the same result” (LHPP 381).Moral theory as an independent, impartial, and systematic inquiry should start, says Sidgwick, with “an examination at once expository and critical, of the different methods of obtaining reasoned convictions as to what ought to be done which are to be found – either explicit or implicit – in the moral consciousness of mankind generally” (Sidgwick 1981, V; and LHPP 381). Such comparison is the only way to reach a “reasoned and satisfactory justification” (LHPP 379) in a domain usually devoid of objectivity. The most significant moral conceptions in the philosophical tradition to be examined and compared are “egoistic hedonism, intuitionism and universal hedonism (the classical utilitarian doctrine)” (LHPP 378–379). There lies the inspiration for Rawls’s own comparative method of justification: justice as fairness should be argued for on the basis of an impartial comparison between utilitarianism, perfectionism and intuitionism drawn by the parties in the original position and endorsed in reflective equilibrium (TJ 42).