§ XV. So, then, these are the two virtues of building: first, the signs of man's own good work; secondly, the expression of man's delight in better work than his own. And these are the two virtues of which I desire my reader to be able quickly to judge, at least in some measure; to have a definite opinion up to a certain point. Beyond a certain point he cannot form one. When the science of the building is great, great science is of course required to comprehend it; and, therefore, of difficult bridges, and light-houses, and harbor walls, and river dykes, and railway tunnels, no judgment may be rapidly formed. But of common buildings, built in common circumstances, it is very possible for every man, or woman, or child, to form judgment both rational and rapid. Their necessary, or even possible, features are but few; the laws of their construction are as simple as they are interesting. The labor of a few hours is enough to render the reader master of their main points; and from that moment he will find in himself a power of judgment which can neither be escaped nor deceived, and discover subjects of interest where everything before had appeared barren. For though the laws are few and simple, the modes of obedience to them are not so. Every building presents its own requirements and difficulties; and every good building has peculiar appliances or contrivances to meet them. Understand the laws of structure, and you will feel the special difficulty in every new building which you approach; and you will know also, or feel instinctively,[32] whether it has been wisely met or otherwise. And an enormous number of buildings, and of styles of buildings, you will be able to cast aside at once, as at variance with these constant laws of structure, and therefore unnatural and monstrous. § XVI. Then, as regards decoration, I want you only to consult your own natural choice and liking. There is a right and wrong in it; but you will assuredly like the right if you suffer your natural instinct to lead you. Half the evil in this world comes from people not knowing what they do like, not deliberately setting themselves to find out what they really enjoy. All people enjoy giving away money, for instance: they don't know _that_,--they rather think they like keeping it; and they _do_ keep it under this false impression, often to their great discomfort. Every body likes to do good; but not one in a hundred finds _this_ out. Multitudes think they like to do evil; yet no man ever really enjoyed doing evil since God made the world. So in this lesser matter of ornament. It needs some little care to try experiments upon yourself: it needs deliberate question and upright answer. But there is no difficulty to be overcome, no abstruse reasoning to be gone into; only a little watchfulness needed, and thoughtfulness, and so much honesty as will enable you to confess to yourself and to all men, that you enjoy things, though great authorities say you should not.