The imitation of Nature, as it presents itself in space and figure, being the real sphere of plastic Invention, it follows, that whatever can occupy a place and be circumscribed by lines, characterised by form, substantiated by colour and light and shade, without provoking incredulity, shocking our conception by absurdity, averting our eye by loathsomeness or horror, is strictly within its province: but though all Nature seem to teem with objects of imitation, the "Choice" of subjects is a point of great importance to the Artist; the conception, the progress, the finish, and the success of his work depend upon it. An apt and advantageous subject rouses and elevates Invention, invigorates, promotes, and adds delight to labour; whilst a dull or repulsive one breeds obstacles at every step, dejects and wearies--the Artist loses his labour, the spectator his expectation. The first demand on every work of art is that it constitute one whole, that it fully pronounce its own meaning, that it tell itself; it ought to be independent; the essential part of its subject ought to be comprehended and understood without collateral assistance, without borrowing its commentary from the historian or the poet; for as we are soon wearied with a poem whose fable and motives reach us only by the borrowed light of annexed notes, so we turn our eye discontented from a picture or a statue whose meaning depends on the charity of a Cicerone, or must be fetched from a book. As the condition that each work of art should fully and essentially tell its own tale, undoubtedly narrows the quantity of admissible objects, singly taken, to remedy this, to enlarge the range of subjects, Invention has contrived by a Cyclus or series to tell the most important moments of a long story, its beginning, its middle, and its end: for though some of these may not, in themselves, admit of distinct discrimination, they may receive and impart light by connection. Of him who undertakes thus to personify a tale, the first demand is, that his Invention dwell on the firm basis of the story, on its most important and significant moments, or its principal actors. Next, as the nature of the art which is confined to the apparition of single moments forces him to leap many intermediate ones, he cannot be said to have invented with propriety, if he neglect imperceptibly to fill the chasm occasioned by their omission; and, finally, that he shall not interrupt or lose the leading thread of his plan in quest of episodes, in the display of subordinate or adventitious beauties. On the observation of these rules depends the perspicuity of his work, the interest we take in it, and, consequently, all that can be gained by the adoption of a historic series. When form, colour, with conception and execution, are deducted from a work, its subject, the unwrought stuff only, the naked materials remain, and these we divide into three classes.