Of course I am talking here of very positively marked men, men of radical idiosyncracy, who have set their stamp and likeness on philosophy and figure in its history. Plato, Locke, Hegel, Spencer, are such temperamental thinkers. Most of us have, of course, no very definite intellectual temperament, we are a mixture of opposite ingredients, each one present very moderately. We hardly know our own preferences in abstract matters; some of us are easily talked out of them, and end by following the fashion or taking up with the beliefs of the most impressive philosopher in our neighborhood, whoever he may be. But the one thing that has COUNTED so far in philosophy is that a man should see things, see them straight in his own peculiar way, and be dissatisfied with any opposite way of seeing them. There is no reason to suppose that this strong temperamental vision is from now onward to count no longer in the history of man's beliefs. Now the particular difference of temperament that I have in mind in making these remarks is one that has counted in literature, art, government and manners as well as in philosophy. In manners we find formalists and free-and-easy persons. In government, authoritarians and anarchists. In literature, purists or academicals, and realists. In art, classics and romantics. You recognize these contrasts as familiar; well, in philosophy we have a very similar contrast expressed in the pair of terms 'rationalist' and 'empiricist,' 'empiricist' meaning your lover of facts in all their crude variety, 'rationalist' meaning your devotee to abstract and eternal principles. No one can live an hour without both facts and principles, so it is a difference rather of emphasis; yet it breeds antipathies of the most pungent character between those who lay the emphasis differently; and we shall find it extraordinarily convenient to express a certain contrast in men's ways of taking their universe, by talking of the 'empiricist' and of the 'rationalist' temper. These terms make the contrast simple and massive.