 Historical research unavoidably requires selectivity in deciding what particular phenomena to emphasize. As Max Weber (1949) notes, there is an infinite depth to historical reality, and therefore it is necessary to select a finite representation of the object of study if we want to approach a problem rigorously. Let us imagine, for example, that a historian is interested in cities and their development over time. This might be pursued as an economic question, a question of regional geography, a question about cultural change, a question about poverty and segregation, a question about municipal governance, or a question about civil disturbances, and so one, for indefinitely many aspects of urban life. One generation of historians may be especially interested in cultural topics, while another generation is preoccupied with the organization of the economy at various points in history. The two orientations lead to very different historical representations of the past. Both inquiries lead to true depictions of the cities in question, but their findings and interpretations are very different. Likewise, the historian needs to make choices about location; is he or she interested in the cities of Britain, the cities of Europe, or all cities in the world? Further, the historian must consider whether to conduct a comparative history of cities, examining similarities and differences in the development of Paris and London; or instead restrict attention to a single case. Simply collecting “historical facts” about cities in the past is not a valid mode of historical inquiry. The question of how historians select and identify their subjects for research is an important one for the philosophy of history, and it has great significance for how we think about “knowing the past”.