The welfare state is not merely a stand-in for missing markets; it can do a whole lot more. When generations overlap and the young must borrow to make educational investments, a dynamically-efficient welfare state, by taxing the middle-aged and offering a compensatory old-age pension, can...

We describe a “business as usual” (BAU) economy in which pollution is a by-product of productive activity by the current generation but “damages” production for future generations. Over time, conditions in the BAU economy become dire: it gets increasingly polluted, consumption falls and...