(_a_) If such information is really to be recognized as art-scholarship,[31] it must be of various kinds and of wide range. The first necessity is an exact acquaintance with the immeasurable region of individual works of art of ancient and modern times, works which in part have actually perished, in part belong to distant countries or portions of the world, or which adverse fortune has withdrawn from one's own observation. Moreover, every work belongs to its _age_, to its _nation_, and to its environment, and depends upon particular historical and other ideas and aims. For this reason art-scholarship further requires a vast wealth of historical information of a very special kind, seeing that the individualized nature of the work of art is related to individual detail and demands special matter to aid in its comprehension and elucidation. And lastly, this kind of scholarship not only needs, like every other, a memory for information, but a vivid imagination in order to retain distinctly the images of artistic forms in all their different features, and especially in order to have them present to the mind for purposes of comparison with other works. (_b_) Within this kind of consideration, which is primarily historical, there soon emerge various points of view which cannot be lost sight of in contemplating a work of art, inasmuch as our judgments must be derived from them. Now these points of view, as in other sciences which have an empirical starting-point, when extracted and put together form universal criteria and rules, and, in a still further stage of formal generalization, _Theories of the arts_. This is not the place to go into detail about literature of this kind, and it may, therefore, suffice to mention a few writings in the most general way. For instance, there is Aristotle's "Poetics," the theory of tragedy contained in which is still of interest; and to speak more particularly, among the ancients, Horace's "Ars Poetica" and Longinus's "Treatise on the Sublime" suffice to give a general idea of the way in which this kind of theorizing has been carried on. The general formulæ which were abstracted by such writers were meant to stand especially as precepts and rules, according to which, particularly in times of degeneration of poetry and art, works of art were meant to be produced. The prescriptions, however, compiled by these physicians of art had even less assured success than those of physicians whose aim was the restoration of health. Respecting theories of this kind, I propose merely to mention that, though _in detail_ they contain much that is instructive, yet their remarks were abstracted from a very limited circle of artistic productions, which passed for _the_ genuinely beautiful ones, but yet always belonged to a but narrow range of art. And again, such formulæ are in part very trivial reflections which in their generality proceed to no establishment of particulars, although this is the matter of chief concern.