The Essay on Criticism is one of Pope's greatest works, and if he had written nothing else, would have placed him among the first critics and the first poets, as it exhibits every mode of excellence that can embellish or dignify didactic composition--selection of matter, novelty of arrangement, justness of precept, splendour of illustration, and propriety of digression. I know not whether it be pleasing to consider that he produced this piece at twenty, and never afterwards excelled it. He that delights himself with observing that such powers may be soon attained, cannot but grieve to think that life was ever after at a stand. To mention the particular beauties of the essay, would be unprofitably tedious; but I cannot forbear to observe that the comparison of a student's progress in the sciences with the journey of a traveller in the Alps, is perhaps the best that English poetry can show. A simile, to be perfect, must both illustrate and ennoble the subject; must show it to the understanding in a clearer view, and display it to the fancy with greater dignity; but either of these qualities may be sufficient to recommend it. In didactic poetry, of which the great purpose is instruction, a simile may be praised which illustrates though it does not ennoble; in heroics that may be admitted which ennobles, though it does not illustrate. That it may be complete, it is required to exhibit, independently of its references, a pleasing image; for a simile is said to be a short episode. To this antiquity was so attentive, that circumstances were sometimes added which, having no parallels, served only to fill the imagination, and produced what Perrault ludicrously called "comparisons with a long tail." In their similes the greatest writers have sometimes failed. The ship race compared with the chariot race, is neither illustrated nor aggrandised; land and water make all the difference. When Apollo, running after Daphne, is likened to a greyhound chasing a hare, there is nothing gained; the ideas of pursuit and flight are too plain to be made plainer, and a god and the daughter of a god, are not represented much to their advantage by a hare and a dog. The simile of the Alps has no useless parts, yet affords a striking picture by itself; it makes the foregoing position better understood, and enables it to take faster hold on the attention; it assists the apprehension, and elevates the fancy.