It is always dangerous, and liable to diminish the clearness of impression, to go over much ground in the course of one lecture. But I dare not present you with a maimed view of this important subject: I dare not put off to another time, when the same persons would not be again assembled, the statement of the great collateral necessity which, as well as the necessity of truth, governs all noble art. That collateral necessity is _the visible operation of human intellect in the presentation of truth, _the evidence of what is properly called design or plan in the work, no less than of veracity. A looking-glass does not design--it receives and communicates indiscriminately all that passes before it; a painter designs when he chooses some things, refuses others, and arranges all. This selection and arrangement must have influence over everything that the art is concerned with, great or small--over lines, over colours, and over ideas. Given a certain group of colours, by adding another colour at the side of them, you will either improve the group and render it more delightful, or injure it, and render it discordant and unintelligible. "Design" is the choosing and placing the colour so as to help and enhance all the other colours it is set beside. So of thoughts: in a good composition, every idea is presented in just that order, and with just that force, which will perfectly connect it with all the other thoughts in the work, and will illustrate the others as well as receive illustration from them; so that the entire chain of thoughts offered to the beholder's mind shall be received by him with as much delight and with as little effort as is possible. And thus you see design, properly so called, is human invention, consulting human capacity. Out of the infinite heap of things around us in the world, it chooses a certain number which it can thoroughly grasp, and presents this group to the spectator in the form best calculated to enable him to grasp it also, and to grasp it with delight.