Brian Barry's justice as impartiality relies upon Thomas Scanlon's contractual device of ‘reasonable rejection’. Many have criticised both Barry and Scanlon for not defining precisely what reasonable is, further suggesting that what is reasonable or rational is culturally specific and cannot underlie a universal account of justice, such as justice as impartiality. In this article I try to uncover the role of rationality, reasons and reasonable agreement in Barry's book Justice as Impartiality, in part by looking back at his first book, Political Argument. I specify in what sense the theory provides a universal account of justice and in what sense it is compatible with weak relativism. I argue that it is a liberal theory in two, very different, senses: first, because of its universalist structure, even though that structure at certain times and places is compatible with what we would now consider as illiberal social justice; second, because it now entails what we see as liberal principles of justice.