All art, after all, is an adventure. In the art of the past the things which directly move our æsthetic emotions are the moments of adventure, the moments at which we join the artist in perceiving intuitively and directly something which we know to be artistically true and beautiful although it is not consistent with the conventional principles on which the art is based. As culture ripens and art becomes a recognized and definite part of our spiritual life, conventions are codified and systematized. In music the classical key system provides us with an obvious example. We acquire the habit of applying our intellectual and reasoning faculties to it. But our æsthetic emotions are not stirred until we are thrown into contact with the irrational. The irrational in this case does not imply utter intellectual chaos and anarchy any more than it does in mathematics or metaphysics. The mathematician perceives a new truth intuitively by an act of imagination, but it is of no use to him until he can prove it by reason; yet reason is of no use to him unless he has creative imagination as well. This imaginative plunge into the irrational is what produces a number of common and elementary physical pleasures, such as the child’s first attempt to walk and such diversions as swimming, riding a bicycle and flying, although all these processes very soon become rational and indeed automatic. We have analogous adventures in the world of art from the beginning. We may say that music is to speech as swimming is to walking. The mind very soon regularizes the new experiences, but the fascination of the arts is that they are always offering us the chance of further ones. We do not enjoy music as an art until we have learned to appreciate it rationally; but at the same time it cannot give us a real æsthetic emotion unless it confronts us forcibly with a further irrational element. It is this irrational reaction which causes us still to be stirred by the music of the past. We listen to a quartet of Mozart; we recognize a familiar convention, we are easily set back into a past cultural period in which Mozart’s language was the language of the day. We understand every phrase, and we may even run the risk of being bored. Suddenly Mozart does something which the average music-maker of his day would not have done; we are thrown off our rational balance, we have to apprehend directly and intuitively. Our minds have to make some unfamiliar movement just as our bodies may in certain circumstances have to make some movement incompatible with normal equilibrium. In the case of bodily movements practical experience and a knowledge of mathematics may subsequently show that this unfamiliar movement is really just as reasonable as walking. Something of the same kind happens in our artistic experience too. Even Mozart may cease to interest us. The once unfamiliar experience becomes automatic, the new harmony becomes a _cliché_.