As conceived in this book, economics is the science of rational choice in a world─our world─in which resources are limited in relation to human wants. The task of economics, so defined, is to explore the implications of assuming that man is a rational maximizer of his ends in life, his satisfactions─what we shall call his “self-interest.†Rational maximization should not be confused with conscious calculation. Economics is not a thoery about consciousness. Behavior is rational when it conforms to the model of rational choice, whatever the state of mind of the chooser.(...) Nor is perfect rationality assumed; rational-choice thoery allows us to assume that rationality is “bounded†because of human cognitive limitations, although another way to think of those limitations is as costs of absorbing and using information.
Richard Posner