No major reform of the welfare state has a chance of going through unless one can make a plausible case as to both its ‘ethical value’ and its ‘economic.value’, that is, that it would have a positive effect in terms of both justice and efficiency. In this essay, this rough conjecture is first presented, and its plausibility probed, on the background of some stylised facts about the rise of modern welfare states in the postwar period. Next, the focus is shifted to the current debate on the introduction of a basic income, a completely unconditional grant paid ex ante to all citizens. It is argued that if basic income is to have a chance of meeting the strong twofold condition stipulated in the conjecture, some major changes are required in the way one usually thinks about justice and efficiency in connection with social policy. But once these changes are made, as they arguably must be, the chance that basic income may be able to meet the challenge is greatly enhanced.