 Third, philosophy of social science. Theorizing about the nature of social reality at least partly involves metaphysically explaining social reality. Debates between (methodological) holists and individualists, for example, concern whether social activities and events are to be explained by appeal to macro-level (social) phenomena, or by the thoughts and actions of the individuals that, most agree, make up or ground those social phenomena (see, e.g., Popper 1945; Watkins 1952). The metaphysically explanatory nature of social theorizing has not always been appreciated. This is brought out in the distinction between explanatory and ontological individualism (Lukes 1968). Explanatory individualism is the thesis that social reality is best explained in terms of individuals, their thoughts and interactions. Ontological individualism, on the other hand, holds that social reality consists in or is exhaustively determined by individuals, their thoughts and interactions. If, however, social reality is or is grounded in individuals and their interactions, social reality is metaphysically explained by those individuals and their interactions (Epstein 2015). Both these theses are theses about explanation.