One of the great defects of traditional morality has been the low estimate it placed upon intelligence. The Greeks did not err in this respect, but the Church led men to think that nothing matters except virtue, and virtue consists in abstinence from a certain list of actions arbitrarily labelled “sin”. So long as this attitude persists, it is impossible to make men realize that intelligence does more good than an artificial conventional “virtue”. When I speak of intelligence, I include both actual knowledge and receptivity to knowledge. The two are, in fact, closely connected. Ignorant adults are unteachable; on such matters as hygiene or diet, for example, they are totally incapable of believing what science has to say. The more a man has learnt, the easier it is for him to learn still more--always assuming that he has not been taught in a spirit of dogmatism. Ignorant people have never been compelled to change their mental habits, and have stiffened into an unchangeable attitude. It is not only that they are credulous where they should be sceptical; it is just as much that they are incredulous where they should be receptive. No doubt the word “intelligence” properly signifies rather an aptitude for acquiring knowledge than knowledge already acquired; but I do not think this aptitude is acquired except by exercise, any more than the aptitude of a pianist or an acrobat. It is, of course, possible to impart information in ways that do not train intelligence; it is not only possible, but easy, and frequently done. But I do not believe that it is possible to train intelligence without imparting information, or at any rate causing knowledge to be acquired. And without intelligence our complex modern world cannot subsist; still less can it make progress. I regard the cultivation of intelligence, therefore, as one of the major purposes of education. This might seem a commonplace, but in fact it is not. The desire to instil what are regarded as correct beliefs has made educationists too often indifferent to the training of intelligence. To make this clear, it is necessary to define intelligence a little more closely, so as to discover the mental habits which it requires. For this purpose I shall consider only the aptitude for acquiring knowledge, not the store of actual knowledge which might legitimately be included in the definition of intelligence.