What do biologists mean when they say that to live is to react? Why was the term abreaction invented and later abandoned by the first generation of psychoanalysts? What is meant by reactionary politics? These are but a few of the questions the internationally renowned scholar Jean Starobinski answers in his conceptual history of the word pair, action and reaction.Not simply a history of ideas, Action and Reaction is also a semantic and philological history, a literary history, a history of medicine, and a history of the biological sciences. By concentrating on the moment when scientific language and ordinary language diverge, Starobinski uncovers a genealogy of the human and natural sciences through their usage of action and reaction as metaphors. Newton's law -- to every action there is an equal and opposite reaction -- becomes a point of departure for an exploration of the lexical and metaphorical traces left in its wake. Starobinski analyzes the scientific, literary, and political effects of the use of the terms action and reaction to describe and explain the material universe, the living body, historical events, and psychological behavior. In what he calls a "polyphonic score" -- a kind of mosaic -- he uses his subject to offer new insights into the work of philosophers (Aristotle, Leibniz, Kant, Nietzsche, Jaspers), scientists (Newton, Bichat, Bernard, Bernheim, Freud), and writers (Diderot, Constant, Balzac, Poe, Valry). Ultimately, the book explores the power and danger of metaphorical language and questions the convergence and collapse of scientific and moral explanations of the universe.