A System of Logic

Mill's first major book and the work that made his reputation, A System of Logic, Ratiocinative and Inductive is a large treatise in six books on reasoning and evidence, written from a thoroughly empiricist standpoint. Book I analyses names and propositions, distinguishing what a term denotes from what it connotes and arguing that proper names denote without connoting. Book II argues that all inference is ultimately from particulars to particulars, and that even the truths of geometry and arithmetic are generalisations from experience. Book III, the heart of the work, treats induction: the uniformity of nature, the law of causation, and the methods of experimental inquiry now known as Mill's methods, including agreement, difference, residues and concomitant variations. Books IV and V cover operations subsidiary to induction, such as classification, and fallacies. Book VI, on the logic of the moral sciences, discusses free will and necessity and asks how a scientific study of character and society might proceed.

It is the classic empiricist account of scientific reasoning, and Mill's methods for finding causes are still taught wherever people learn how to test a causal claim.