It is difficult to define exactly the difference between the early work of a poet (or of a dramatist in verse) and his later work. In fact any general definition is impossible, for poets vary. Some merely dry up and go on writing from habit; others change their style consciously and deliberately, others unconsciously—but all change. Anyone who has thought about and read poetry will agree that if a poet lives long enough, his work is bound to change. Any Shakespeare scholar can distinguish by style alone, not to mention other evidence, Shakespeare's Two Gentlemen of Verona from his Tempest. Similarly, any competent critic will admit that Milton could not have written Lycidas or his Ode on the Morning of Christ's Nativity after he wrote Paradise Lost. Again Dante could not have written the poems in his Vita Nuova after he finished the Divine Comedy. In both cases some people prefer the earlier poems. A poet does not always improve with years, but his mind changes gradually and his work reflects that.

Poets differ so much that we are usually content to enjoy their works without noticing their order. But it is not always possible to ignore it. A fragmentary papyrus has lately been discovered which appears to be the remains of an extract from the Didascaliae prefixed to a play of Aeschylus. It states that Aeschylus was victorious with a group of plays which contained the Danaides and Amymone, and that Sophocles was second. As it is generally agreed that the Supplices belonged to the same group as the plays mentioned it can be assumed with confidence that this name was to be found on the part of the papyrus now missing.