The basic question in political science is: what causes such and such a political phenomenon? ‘Studying Politics Scientifically’ shows that political science requires that we forget about individual differences and construe politics, over time, as a process, analogous to what happens in nature. The idea of a system, that is, a set of mechanical components having a fixed relation to each other, is central to conceiving of politics scientifically. One difficulty with this is deciding on the boundaries between the endogenous (internal) and the exogenous (external) factors. Where does the system end and the outside manipulative intelligence begin? Rational choice theory and irrational human behaviour are also discussed.