I have already adverted to the influence which taste, and the other faculties and powers and endowments of the mind, exercise on its different operations. Imagination is in an equal and a corresponding manner thus affected, both as to its extent and its mode of acting. As already observed, each of the different faculties and capacities of the mind aid the other, and they do so in almost every operation which the mind performs, in the same way as the different members of the body, although varying from each other as to their nature and end, either directly or indirectly assist one another in most of their efforts. Thus, the reason aids the imagination, and the imagination often assists the reason ; and the faculty by which we receive ideas, aids them both. Taste too aids both the imagination and the reason. In each of these cases the faculty or capacity peculiarly adapted to effect the effort in question, is that which takes the lead in accomplishing it, while the others only assist and direct it in its career. Thus reason aids imagination in two opposite modes. 1. By directing and pointing out suitable exercises of this power. 2. By correcting its operations, and preventing it from running into extravagance. Hence the result of the aid, and of the action of the reason is not to weaken, but to add force to the efforts of imagination. It directs them to a proper aim, instead of suffering them to shoot at random. As regards its influence on the imaginative operations, reason is indeed the exact counterpart of passion. In the exercise of imagination, while passion acts as a sail, reason serves as a rudder to prevent the mind from running into extravagance. Hence, the province of reason in efforts of an imaginative kind, although its sphere may be apparently very humble and only subordinate, is nevertheless highly important, and even indispensable. The helmsman who stands at the rear of the vessel, has no claim to the merit of helping it forward, of assisting in its machinery to propel it through the waves, or of aiding to turn the sails so as to catch the breeze which urges it onward along the watery road; yet it is by the rudder that its progress is kept straight, and by means of which rocks and shoals are avoided, the slightest collision with which would not only arrest its career, but even plunge it beneath the waves, and involve it in instant ruin.
But although reason is frequently exercised in the earlier stages of the operation of imagination, and will then point out the extravagances into which we are running, and thus, to a certain extent occasionally impede the imaginative process ; yet when, by the excitement of the various passions and emotions a certain amount of obscurity is thrown over the whole design, so that its mechanism is as it were veiled from our scrutiny, and we lose sight of the mode in which the object before us was constructed, our feelings impel us irresistibly forward in spite of the remonstrances of reason, until at length the very reason itself becomes dragged along by the current, and, like a tree torn up and driven down a torrent, it adds fury to the stream instead of aiding to restrain its impetuosity.