"In pursuing the analogies here I considered, it is necessary to compare mere art with art--the form, as such, of the one, with the form of the other. Thus, in comparing sculpture and poetry together, the parallel conditions are to be sought in the strictly corresponding departments. As sculpture, in reference to nature, (to repeat an observation before made,) gives substance for substance, so poetry gives words for words. Accordingly, the form of poetry is by agreement or convention (similar in principle to that which dictates the conditions of sculpture) effectually distinguished from the form of ordinary language. And it will now be seen that the limitations of poetry, in such outward characteristics, are more definite and more comprehensive than those of sculpture; for whereas the material of marble may sometimes coincide literally with that of substances in nature, the form of poetry never can entirely coincide with that of ordinary language. This greater liability of sculpture to be confounded with reality certainly adds to its difficulty, since the doubtful cases, which may be left to the taste of the sculptor, are often settled by an immutable rule for the poet." Whoever would desire a knowledge of the original causes of the differences of alto, basso, and mezzo relievo, should read the admirable treatise on the subject. They are not to be confounded as arising from the same conditions, and subject to the same rules. The differences of position and light, by their distinct requirements, separate the three styles of relievo, the alto, basso, and mezzo. It is not, as many suppose, that the basso, the lower relief, is less finished than the alto, or high relief; the finish of each is differently placed. "In the highest relief, however decided the shadows may, and must of necessity be, on the plane to which the figure is attached, the light on the figure itself is kept as unbroken as possible; and this can only be effected by a selection of open attitudes; that is, such an arrangement of the limbs as shall not cast shadows on the figure itself. In basso-relievo, the same general effect of the figure is given, but by very different means: the attitude is not selected to avoid shadows on the figure, because, while the extreme outline is strongly marked, the shadows within it may be in a great measure suppressed; so that the choice of attitudes is greater. Mezzo-relievo differs from both; it has neither the limited attitudes of the first, nor the distinct outline and suppressed internal markings of the second: on the contrary, the outline is often less distinct than the forms within it, and hence it requires, and is fitted for, near inspection. Its imitation may thus be more absolute, and its execution more finished, than those of the other styles."