Three meanings of ‘rationalism’

1. The theory of knowledge held by the so-called ‘rationalist’ philosophers – René Descartes, Benedict Spinoza and Gottfried Leibniz – which was that the general nature of the world can be established a priori * by (non-empirical) demonstrative reason. The theory implies that concepts are derived not from experience but from reasoning.

In this sense it is the opposite of empiricism (the theory of e.g. John Locke and David Hume), which holds that all knowledge comes from experience.

2. The philosophical position that one’s beliefs and conduct should be based on a combination of experience and reason (of both the inductive and deductive kinds). Thus in this sense it actually embraces empiricism.

Its opposite in this sense is irrationalism, of which there are two types:

Descriptive irrationalism, which holds that the beliefs and conduct of human beings are not (as a matter of empirical fact) guided by reason, but rather by, e.g.:

1. The unconscious: libido/id & superego (Sigmund Freud);
2. False consciousness engendered by economic position (Karl Marx);
3. Educational, cultural and social background (Karl Mannheim).

Normative irrationalism, which holds that the beliefs and conduct of human beings ought not (as a matter of deliberate choice) be guided by reason, but rather ought to be guided by, e.g.:

1. Sentiment and natural impulse (Jean Jacques Rousseau);
2. A recognition of the absurdity of life (Sören Kierkegaard);
3. The Life Force (Friedrich Nietzsche);
4. Primal instinct (DH Lawrence).

3. Disbelief in the supernatural, and in particular ‘god’; in this sense it is more or less synonymous with atheism.

People who describe themselves as ‘rationalists’ today and who join the Rationalist Society of Australia would be rationalists in either sense 2 or sense 3 or both. Although some of them may in fact acknowledge the limitations to reason exposed by e.g. Freud, Marx and Mannheim, they would claim that these can be eliminated or at least minimised by e.g. psychoanalysis, political action and self-awareness.