It is the function of architecture to reveal also the nature of light. For the light is intercepted, confined, and reflected by the mass of the building. It is thrown into high relief by the receding forms, which supply the contrasting depths of shade. It thus unfolds its nature and qualities in the clearest and most definite way. It is not merely form and symmetry which appeal to us in architecture, but primarily the fundamental forces of nature, the simplest qualities of matter. The quality of the material, therefore, is of great importance. The fundamental law of architecture is that no burden shall be without sufficient support, and no support without a suitable burden. The purest example of this principle is the column and entablature. In separating completely the support and burden in the column and entablature, the reciprocal action of the two and their relation to each other become perfectly clear. For this reason the simplest building in Italy gives æsthetic pleasure, due to the flatness of the roof. A high roof is neither support nor burden, for its two halves support each other. It serves merely a useful end, presenting to the eye an extended mass, which is wholly alien to the æsthetic sense. Architecture requires large masses, in order to be felt adequately, and it must work out its own character under the law of the most perfect clearness to the eye. It exists in space-perception, and must make a direct and inevitable appeal to the æsthetic sense. This demands symmetry, which is necessary to mark out the work as a whole. It is only through symmetry that a work of architecture reveals itself as {70} an organic unity and as the development of a central thought. Architecture ought not to imitate the forms of nature, and yet it should work in the spirit of nature. It should reveal the end in view quite openly, and should avoid everything which is merely aimless. Thus it achieves the grace which is the result of ease, and the subordination of every detail to its purpose. It follows from Schopenhauer's treatment of architecture that he held Greek work of the best period to be the highest type of building which it is possible to attain. In its best examples that style is perfect and complete, and is not susceptible of any important improvement. The modern architect, he held, cannot depart, to any great extent, from the rules and models of the Greeks, without descending the path of deterioration. There remains nothing for him to do but to apply the art transmitted to him, and to carry out the rules laid down, so far as he is able under the limitations of climate, age, and country.