Even in the most ancient cases, where it would be supposed that opinion would finally have crystallized, we observe curious oscillations. Homer, it is true, is accepted by all critics, in all nations, as the final standard of what is admirable in heroic narrative poetry, and has for centuries been so accepted. But what is the standard of Greek tragedy? The study of classic criticism will show us that the standard has been incessantly shifting from Æschylus to Sophocles and on to Euripides and back again to Æschylus. If we wish to point to an authoritative type, we must consider this triad as one, since no two generations agree as to their comparative, though all to their positive merit. In like manner, the relative value of Virgil and Theocritus, of Horace and Catullus, is always shifting, according as the quality of the one or of the other happens to appeal to one or to another habit of modern thought. Yet antiquity obviously provides us with a standard of bucolic poetry, and another of subjective and semi-social lyric, each of them settled now beyond any probability of decay. People will go on preferring Theocritus to Virgil, or Virgil to Theocritus, but no rational person is likely to question again the excellence of the species of art of which these two are the leading exponents. So there are those who prefer Dryden to Pope, or Coleridge to Wordsworth, and to whom neither seem to present the complete practitioner of a system. Yet no one denies, and it grows increasingly probable that no one will ever deny, the authority of the Pope-Dryden or of the Wordsworth-Coleridge standard of excellence, final and unquestionable, in a particular department. Opinion, that is to say, wavers as to the individual long after it has irrevocably accepted the type.