 Similarly, economists of the 19th century tended to pose explanations "a priori", and reject disconfirmation by posing circuitous routes of reasoning to maintain their "a priori" laws.In 1843, Mill's "A System of Logic" introduced Mill's methods, explaining the five principles whereby causal laws can be discerned to enhance the empirical sciences as, indeed, the inductive sciences.For Mill, all explanations have the same logical structure, while society can be explained by natural laws.