 Many political philosophers take (some of) the criticisms raised against markets (cf. 3.2 above) seriously. They therefore argue that markets can only be justified if they coexist with other institutions that supplement or correct their outcomes. These institutions can be subdivided into different categories. Economists typically use the concept of “market failure” to describe cases where one or more conditions for efficient market outcomes are not met, e.g., when there are externalities or public goods (see e.g., Bator 1958; Cowen 1988). To improve outcomes in such cases can require the regulation of markets (e.g., by prohibiting negative externalities such as the emission of harmful pollutants) or the provision of public goods by state institutions. Rules and regulations might also be needed – and can be justified from the point of view of Pareto efficiency – in cases of what Basu (2007) has called the “large number problem”: some form of behavior, although harmless in itself, may have a negative impact if committed by a large number of people. The same can be true when there is more than one equilibrium in a market and it is desirable to move to one of them rather than another, e.g., from an equilibrium with child labor to one without (Basu / Van 1998). One might also argue that the macro-economic stabilization of markets, for example through the central bank or through measures that raise demand in recessions (cf. Keynes 1936), belongs into the category of provision of public goods. The effectiveness of such measures, however, is deeply contested among economists.