From John Rawls, A Theory of Justice. First, read the whole selection (on electronic reserves) as background. Then focus on:

(a) p. 252, the three paragraphs that begin, "Kant held, I believe, that a person is acting autonomously . . . ."

(b), p. 256, "The original position may be viewed . . . however much a single self might be of a mind to opt for them."