 Another important strand of thinking within analytic philosophy has focused attention on historical ontology (Hacking 2002, Little 2010). The topic of historical ontology is important, both for philosophers and for practicing historians. Ontology has to do with the question, what kinds of things do we need to postulate in a given realm? Historical ontology poses this question with regard to the realities of the past. Should large constructs like ‘revolution’, ‘market society’, ‘fascism’, or ‘Protestant religious identity’ be included in our ontology as real things? Or should we treat these ideas in a purely nominalistic way, treating them as convenient ways of aggregating complex patterns of social action and knowledge by large numbers of social actors in a time and place? Further, how should we think about the relationship between instances and categories in the realm of history, for example, the relation between the French, Chinese, or Russian Revolutions and the general category of ‘revolution’? Are there social kinds that recur in history, or is each historical formation unique in important ways? These are all questions of ontology, and the answers we give to them will have important consequences for how we conceptualize and explain the past.