I know it may be urged in defence of Horace that this unity is not necessary, because the very word _satura_ signifies a dish plentifully stored with all variety of fruits and grains. Yet Juvenal, who calls his poems a _farrago_ (which is a word of the same signification with _satura_), has chosen to follow the same method of Persius and not of Horace; and Boileau, whose example alone is a sufficient authority, has wholly confined himself in all his satires to this unity of design. That variety which is not to be found in any one satire is at least in many, written on several occasions; and if variety be of absolute necessity in every one of them, according to the etymology of the word, yet it may arise naturally from one subject, as it is diversely treated in the several subordinate branches of it, all relating to the chief. It may be illustrated accordingly with variety of examples in the subdivisions of it, and with as many precepts as there are members of it, which all together may complete that _olla_ or hotch-potch which is properly a satire. Under this unity of theme or subject is comprehended another rule for perfecting the design of true satire. The poet is bound, and that _ex officio_, to give his reader some one precept of moral virtue, and to caution him against some one particular vice or folly. Other virtues, subordinate to the first, may be recommended under that chief head, and other vices or follies may be scourged, besides that which he principally intends; but he is chiefly to inculcate one virtue, and insist on that. Thus Juvenal, in every satire excepting the first, ties himself to one principal instructive point, or to the shunning of moral evil. Even in the sixth, which seems only an arraignment of the whole sex of womankind, there is a latent admonition to avoid ill women, by showing how very few who are virtuous and good are to be found amongst them. But this, though the wittiest of all his satires, has yet the least of truth or instruction in it; he has run himself into his old declamatory way, and almost forgotten that he was now setting up for a moral poet. Persius is never wanting to us in some profitable doctrine, and in exposing the opposite vices to it. His kind of philosophy is one, which is the Stoic, and every satire is a comment on one particular dogma of that sect, unless we will except the first, which is against bad writers; and yet even there he forgets not the precepts of the “porch.” In general, all virtues are everywhere to be praised and recommended to practice, and all vices to be reprehended and made either odious or ridiculous, or else there is a fundamental error in the whole design.