Book excerpt: The Ideal of Rationality presents an evaluation of all the main varieties of rationalism, in clear and jargon-free language. Different notions of rationality - such as means-end, conception, hedonism, and the evil-avoidance view - are examined and rejected, in favor of the theory that to act rationally is to 'act for the best', a theory Nathanson characterizes as "critical pluralism". Among present-day thinkers whose ideas are scrutinized are Richard Brandt, Bernard Gert, Gilbert Harman, John Kekes, Robert Nozick, Karl Popper, and John Rawls.