ABSTRACT
In science, as in every kind of study, knowledge already acquired facilitates the acquisition of further knowledge. The combination of deduction with induction has been named, by John Stuart Mill, the “Deductive Method”; but as this is rather liable to be confused with mere deduction, which is only one constituent of the combined method, it may be better to describe it as the Deductive-Inductive Method. An interesting example of the use of the Deductive-Inductive Method is contained in Herbert Spencer’s Principles of Sociology. If inductive inference sometimes needs support from deduction, purely deductive reasoning stands in even greater need of inductive confirmation, especially in the case of complex phenomena. The history of science, especially of economic and social science, can point to many cases which should serve as a warning in this respect. Ricardo, for instance, arguing deductively, maintained that the continuous increase in population would necessitate the cultivation of less and less fertile soils.
