Burke's chief claim to a permanent place among thinkers lies in his critical rejection of eighteenth-century rationalism in political philosophy, and the general character of this I may assume to be sufficiently familiar not to need exposition. The true virtue in politics, according to Burke, is not metaphysical reasoning, but practical tact and prudence. Go slow, build on the past, avoid sweeping changes, take the "precautions which distinguish benevolence from imbecility"'-this is the substance of his teaching. As my purpose is largely polemical, I should make it clear at the start that I have no quarrel with such a position in a general way. As a controversialist, Burke must be allowed to have had considerably the better of the argument. Indeed, were it not that overconfidence in reasoned theories of society running far ahead of practice continues to be much in evidence, one might consider it hardly necessary to raise again the question of the validity, within certain limits, of his justification of expediency versus theory. But the limits would still remain to be determined. For however valid in itself, Burke's doctrine may become the starting-point of very opposite social attitudes according as it is held. The difference of emphasis may be suggested by the two words experience and experiment. The one of these looks chiefly to the past, the other chiefly to the future; but it is not unnatural to take them at times as interchangeable. Now the major part at least of what is most valuable in Burke's philosophy is covered by the word "experiment." To say that politics should be experimental is to imply that it should never "entirely and at once depart from antiquity." But a philosophy of "experience" may also have the sense, not that we should