[H]istory and the social sciences crystalized out of a single field of discourse. It was only between the 1880s and World War I that sociology, history, political science, anthropology, geography, and economics emerged as the distinct and professionalized academic disciplines we know today. Prior to that time, intellectual discussion flowed easily across the indistinct boundaries between different genres of scholarship. It is difficult to assign major thinkers of this era to a single field, as we understand these fields today. Was Adam Smith or John Stuart Mill a philosopher, an economist, or a political scientist? Was Marx an economist, a sociologist, a philosopher, or a historian? Tocqueville a historian, a sociologist, an ethnographer, or a political scientist?

—William H. Sewell, Jr., Logics of History, (Chicago: The University of Chicago Press, 2005), 2.