A final remark. Justice as fairness is not a complete contract theory. For it is clear that the contractarian idea can be extended to the choice of more or less an entire ethical system, that is, to a system including principles for all the virtues and not only for justice. Now for the most part I shall consider only principles of justice and others closely related to them; I make no attempt to discuss the virtues in a systematic way. Obviously if justice as fairness succeeds reasonably well, a next step would be to study the more general view suggested by the name "rightness as fairness." But even this wider theory fails to embrace all moral relationships, since it would seem to include only our relations with other persons and to leave out of account how we are to conduct ourselves toward animals and the rest of nature. I do not contend that the contract notion offers a way to approach these questions which are certainly of the first importance; and I shall have to put them aside. We must recognize the limited scope of justice as fairness and of the general type of view that it exemplifies. How far its conclusions must be revised once these other matters are understood cannot be decided in advance.
(John Rawls, A Theory of Justice, rev. ed. [Cambridge: Harvard University Press, Belknap Press, 1999], 15 [first edition published in 1971])