234. Hence, we see the grand importance of the choice of our means of enhancing effect, and we derive the simple rule for that choice, namely, that, when we wish to increase abstract impression, or to call upon the sympathy of the spectator, we are to use contrast; but, when we wish to extend the operation of the impression, or to awaken the selfish feelings, we are to use assimilation. This rule, however, becomes complicated, where the feature of contrast is not altogether passive; that is, where we wish to give a conception of any qualities inherent in that feature, as well as in what it relieves; and, besides, it is not always easy to know whether it will be best to increase the abstract idea, or its operation. In most cases, energy, the degree of influence, is beauty; and, in many, the duration of influence is monotony. In others, duration is sublimity, and energy painful: in a few, energy and duration are attainable and delightful together. 235. It is impossible to give rules for judgment in every case; but the following points must always be observed:--First, when we use contrast, it must be natural and likely to occur. Thus the contrast in tragedy is the natural consequence of the character of human existence; it is what we see and feel every day of our lives. When a contrast is unnatural, it destroys the effect it should enhance. Canning called on a French refugee in 1794. The conversation naturally turned on the execution of the Queen, then a recent event. Overcome by his feelings, the Parisian threw himself upon the ground, exclaiming, in an agony of tears, "La bonne reine! la pauvre reine!" Presently he sprang up, exclaiming, "Cependant, Monsieur, il faut vous faire voir mon petit chien danser." This contrast, though natural in a Parisian, was unnatural in the nature of things, and therefore injurious. 236. Secondly, when the general influence, instead of being external, is an attribute or energy of the thing itself, so as to bestow on it a permanent character, the contrast which is obtained by the absence of that character is injurious, and becomes what is called an interruption of the unity. Thus, the raw and colorless tone of the Swiss cottage, noticed in Sec. 42, is an injurious contrast to the richness of the landscape, which is an inherent and necessary energy in surrounding objects. So, the character of Italian landscape is curvilinear; therefore, the outline of the buildings entering into its composition must be arranged on curvilinear principles, as investigated in Sec. 144.