But how are we to decide what is the most favoured interpretation? I assume, for one thing, that there is a broad measure of agreement that principles of justice should be chosen under certain conditions. To justify a particular description of the initial situation one shows that it incroporates these commonly shared presumptions. One argues from widely accepted but weak premised to more specific conclusions. Each of the presumptions should by itself be natural and plausible; some of then may seem innocuous or even trivail. The aim of the contract approach is to establish that taken together they impose significant bounds on acceptable principles of justice. The ideal outcome would be that these conditions determine a unique set of principles; but I shall be satisfied if they suffice to rank the main traditional conceptions of social justice.