In any notice of the historical development of ornamental art, the concurrent styles of architecture should, in their general features at least, be illustrated, for it is not always possible to divorce ornament from architecture, and it is hardly possible to design or construct good ornament otherwise than according to the laws that govern good architecture. Of course, we must admit that some very beautiful ornament, or rather decoration, has been designed otherwise than on architectural lines, but this kind of decoration has its beauty of technique and execution to recommend it, rather than its constructive qualities. Chinese and Japanese ornament will occur to the reader as examples of this kind of work, but the best ornament the world has ever seen has been constructed and is based on the laws that govern good architecture. Some of these laws, such as stability, repose, variety, and proportion, are derived from nature. As all architectural styles, however, possess them more or less in common, we must look elsewhere for the sources from which the peculiar characteristics that distinguish the styles are developed and derived. The causes and forces are so subtle and the developments so gradual, that it is almost impossible to arrive at a satisfactory explanation, as religions, inventive faculty, and symbolism play an important _rôle_ in style development. It is rather to the inventive faculties of man, than to hints supplied by nature, that we must look for the origin and development of what is called style in architecture or ornament. In every case this is arrived at by a slow process, and by the extensive and persistent use of distinguishing features selected according to the needs and requirements of the time, to satisfy the prevailing tastes. “Style” is then the something that man has invented or created; it may be called the soul of architecture, without which, a building, however pretentious, ceases to exist as an artistic conception. Apart from the greatest or more striking features in the various divisions of historic architecture, such as the horizontal beam in Greek, the round arch in Roman and Romanesque, the pointed arch in Gothic and Mohammadan buildings, there are the mouldings that are so important in determining the period—they alone of themselves will often determine the style or date of a building—and these features, above all others, are the least derived from nature. On the other hand, the decoration of mouldings, though suggested by their contours, is generally derived from natural forms.