 In the years before World War I, Łukasiewicz worked predominantly on matters to do with the methodology of science. His doctorate, published in 1903 as “On induction as the inverse of deduction”, investigated the relationship between the two forms of reasoning, in the light of work by Jevons, Sigwart and Erdmann. Inductive reasoning, proceeding from singular empirical statements, attempts on his early view to reach a general conclusion to which a certain probability can be ascribed. But he soon shifted to the view that it is impossible to ascribe a determinate probability to a general statement on the basis of induction. Rather the method of the empirical sciences is to creatively hazard the thought that a certain generalization is true, deduce singular conclusions from this, and then see whether these are true. If one conclusion is not, then the general statement is refuted. This, an early formulation of the hypothetico-deductive method of science, anticipates the ideas of Popper by more than two decades, though expressed less forcefully. Łukasiewicz also anticipated Popper by stressing what he called “creative elements in science”, against the idea that the scientist’s task is to reproduce or replicate the facts.