THE WORD philosophy means the love of wisdom, but what philosophers really love is reasoning. They formulate theories and marshal reasons to support them, they consider objections and try to meet these, they construct arguments against other views. Even philosophers who proclaim the limitations of reason—the Greek skeptics, David Hume, doubters of the objectivity of science—all adduce reasons for their views and present difficulties for opposing ones. Proclamations or aphorisms are not considered philosophy unless they also enshrine and delineate reasoning.
One thing philosophers reason about is reasoning itself. What principles should it obey? What principles must it obey? Aristotle initiated the explicit formulation and study of deductive principles, writers on science and probability theory delineated modes of nondeductive reasoning and support, Descartes attempted to show why we should trust the results of reasoning, Hume questioned the rationality of our doing so, and Kant demarcated what he held to be reason's proper domain. This delineation of reason was not an academic exercise. Discoveries were to be applied: people's reasoning was to be improved, their beliefs and practices and actions made more rational. Inquiring into the rationality of contemporary beliefs and practices carries risks, Socrates discovered. The traditions of a society sometimes do not withstand scrutiny; not everyone wishes to see the implicit examined explicitly. Even the simple consideration of alternatives can seem a corrosive undercutting of what actually exists, an exposure of arbitrariness.
Rationality fixed human distinctiveness, the Greeks held. “Man is a rational animal.” The capacity to be rational demarcates humans from other animals and thus defines them. Human specialness has repeatedly been contracted since the Middle Ages—this was the first large statement about intellectual history that I recall reading. Copernicus, Darwin, and Freud taught us that human beings do not occupy a special place in the universe, they are not special in their origin and are not always guided by rational or even consciously known motives. What continued to give humanity some special status, though, is its capacity for rationality. Perhaps we do not consistently exercise this valuable attribute; yet it sets us apart. Rationality provides us with the (potential) power to investigate and discover anything and everything; it enables us to control and direct our behavor through reasons and the utilization of principles.