But beside these general advantages, which the Philosophy of Mind extends to all the inquiries of which human genius is capable, there are some advantages more peculiarly felt in certain departments of science or art. It is not merely _with_ the mind that we operate; the subject of our operations is also often the _mind itself_. In education, in criticism, in poetry, in eloquence, the mind has to act upon mind, to produce in it either emotions that are _temporary_, or affections and opinions that are _permanent_. We have to instruct it,--to convince it,--to persuade it,--to delight it,--to soften it with pity,--to agitate it with terror or indignation;--and all these effects, when other circumstances of genius are the same, we shall surely be able to produce more readily, if we know the natural laws of thought and emotion; the feelings which are followed by other feelings; and the thoughts, which, expanding into other thoughts, almost of themselves produce the very passion, or conviction, which we wish to excite. “One considerable advantage,” says Mr Hume, “which results from the accurate and abstract philosophy, is its subserviency to the easy and humane; which, without the former, can never attain a sufficient degree of exactness in its sentiments, precepts, or reasonings. All polite letters are nothing but pictures of human life in various attitudes and situations; and inspire us with different sentiments of praise or blame, admiration or ridicule, according to the qualities of the object which they set before us. An artist must be better qualified to succeed in this undertaking; who, besides a delicate taste and quick apprehension, possesses an accurate knowledge of the internal fabric, the operations of the understanding, the workings of the passions, and the various species of sentiment which discriminate vice and virtue. However painful this inward search or inquiry may appear, it becomes, in some measure, requisite to those who would describe with success the obvious and outward appearances of life and manners. The anatomist presents to the eye the most hideous and disagreeable objects; but his science is highly useful to the painter in delineating even a Venus or an Helen. While the latter employs all the richest colours of his art, and gives his figures the most graceful and engaging airs, he must still carry his attention to the inward structure of the human body, the position of the muscles, the fabric of the bones, and the use and figure of every part or organ. Accuracy is, in every case, advantageous to beauty, and just reasoning to delicacy of sentiment;--in vain would we exalt the one by depreciating the other.”[11]