I think most philosophers of science would say that all scientific generalizations are probabilistic rather than logically certain, more so for the social sciences because the systems you are studying are more complex than, say, molecules, and because there are fewer opportunities to intervene experimentally and to control every variable. But the existence of the social sciences, including psychology, to the extent that they have discovered anything, shows that, despite the uncontrollability of human behavior, you can make some progress: you can do your best to control the nuisance variables that are not literally in your control; you can have analogues in a laboratory that simulate what you’re interested in and impose an experimental manipulation. You can be clever about squeezing the last drop of causal information out of a correlational data set, and you can use converging evidence, the qualitative narratives of traditional history in combination with quantitative data sets and regression analyses that try to find patterns in them. But I also go to traditional historical narratives, partly as a sanity check. If you’re just manipulating numbers, you never know whether you’ve wandered into some preposterous conclusion by taking numbers too seriously that couldn’t possibly reflect reality. Also, it’s the narrative history that provides hypotheses that can then be tested. Very often a historian comes up with some plausible causal story, and that gives the social scientists something to do in squeezing a story out of the numbers.