"The idea for the present work came to me, perhaps appropriately, on April Fools' Day, 2017, at the conclusion of a meeting in Cologne of the International Sociological Association Research Committee 28 on Social Stratification and Mobility. Some months previously, I had published a book, Sociology as a Population Science, in which my main concern was, as I put it (2016: 2), 'not to propose to sociologists how they should conceive of and practise their subject' but rather 'to suggest a way in which a fuller and more explicit rationale than has hitherto been available might be provided for what a large and steadily growing number of sociologists already do - although, perhaps, without a great deal of reflection on the matter'. What I argued was that most of those who shared in the goal of developing sociology as a science were in effect pursuing sociology as a population science, in a sense that I sought to explain. What was essentially involved was studying human populations across time and place by abstracting from the particular histories and attributes of their individual members in all their variability in order to focus on the - probabilistic rather than law-like - regularities in social life that were the properties of these populations themselves"--