The importance of maintaining the unity of the subject in artistical composition of each kind, has already been demonstrated in the preceding chapter. No less essential is the preservation of unity of action among all the different personages in a transaction which forms the topic of artistical description or narration. Indeed, however busily engaged the several individuals represented in a composition of this kind may appear to be, and however various the nature of the different actions carried on, it is of essential importance that a strict and complete unity of action and co-operation should pervade and control the whole. Like the different soldiers of a regiment engaged in conflict, although each, to a certain extent, acts by himself independently, yet they all act in concert together, all obey the same word of command, and the efforts of all are alike directed to the attainment of the same object. Or the principle and operation of unity of action in pictorial composition, may be perhaps best illustrated by that of tune in music. Here a variety of instruments of different kinds, and of voices as well, may all be sounding together; yet, however dissimilar in character, they all tend to produce, and all harmonize in one tune. So in pictorial composition, there may be many different characters, who are more-over represented as engaged in occupations of a very different nature; but they should all conduce to telling the same story, and should each aid in the general effect which the composition, as a whole, is intended to produce.
Nevertheless, this unity of action, as regards the general regulation of the composition, is not by any means intended to exclude the introduction of episodes or minor independent events which, however, should at the most but vary or relieve, and ought never to counteract or interfere with the main trans-action. As in composition, one principal figure is the leading personage in the piece to which all the others are subordinate, and to whose effect they add; so in narration, one particular action is that which is represented, the effect of which all the minor operations contribute to aid.
This principle is applicable to, and is required to be maintained in descriptions in painting and sculpture, as well as in those in poetry and eloquence, in music and in acting. As regards architecture, and costume, and gardening, the same directions cannot of course be deemed strictly suitable to these arts, for preserving general unity in the designs of which the rules already referred to must suffice.