As to poetry other than dramatic, the Restoration critics were at one in judging blank verse too "low" for a poem of heroic dimensions; and though Addison gave it the preference in epic poetry, Johnson was its persistent foe, and regarded it as little short of immoral. But for that matter, Gray could endure no blank verse outside of Milton. This is curious, that rhyme, a mediaeval invention, should have been associated in the last century with the classical school of poetry; while blank verse, the nearest English equivalent of the language of Attic tragedy, was a shibboleth of romanticizing poets, like Thomson and Akenside. The reason was twofold: rhyme came stamped with the authority of the French tragic alexandrine; and, secondly, it meant constraint where blank verse meant freedom, "ancient liberty, recovered to heroic poem from the troublesome and modern bondage of rhyming."[26] Pope, among his many thousand rhymed couplets, has left no blank verse except the few lines contributed to Thomson's "Seasons." Even the heroic couplet as written by earlier poets was felt to have been too loose in structure. "The excellence and dignity of it," says Dryden, "were never fully known till Mr. Waller taught it; he first made writing easily an art; first showed us how to conclude the sense most commonly in distichs, which, in the verse of those before him, runs on for so many lines together, that the reader is out of breath to overtake it."[27] All through the classical period the tradition is constant that Waller was the first modern English poet, the first correct versifier. Pope is praised by Johnson because he employed but sparingly the triplets and alexandrines by which Dryden sought to vary the monotony of the couplet; and he is censured by Cowper because, by force of his example, he "made poetry a mere mechanic art." Henceforth the distich was treated as a unit: the first line was balanced against the second, and frequently the first half of the line against the second half. "To err is human, to forgive divine." "And so obliging, that he ne'er obliged." "Charms strike the eye, but merit wins the soul," etc., etc. This type of verse, which Pope brought to perfection, and to which he gave all the energy and variety of which it was capable, so prevailed in our poetry for a century or more that one almost loses sight of the fact that any other form was employed. The sonnet, for instance, disappeared entirely, until revived by Gray, Stillingfleet, Edwards, and Thomas Warton, about the middle of the eighteenth century.[28] When the poets wished to be daring and irregular, they were apt to give vent in that species of pseudo-Pindaric ode which Cowley had introduced--a literary disease which, Dr. Johnson complained, infected the British muse with the notion that "he who could do nothing else could write like Pindar."