 According to Aristotle, deductive logic (especially in the form of the syllogism) plays a central role in the articulation of scientific understanding, deducing observable phenomena from definitions of natures that hold universally and without exception. However, in the practical matters of everyday life, we rely upon generalizations that hold only “for the most part”, under normal circumstances, and the application of such common sense generalizations involves merely dialectical reasoning, reasoning that is defeasible and falls short of deductive validity. Aristotle lays out a large number and great variety of examples of such reasoning in his work entitled the Topics.