The achievement of creation becomes the more conspicuous on review of what the story had been.[31] Mere unrelated episodes of the older sources, mere scattered incidents in Benoît’s huge _Roman de Troie_, had kindled Boccaccio’s _Filostrato_. Of its 5512 lines Chaucer used 2730, or about half, but carried his own story to 8239. His addition, most of the first half of his story, is devoted to the gradual yielding of Cressid. Boccaccio has no such approach because he has no such person. His story is of Troilus; and his Cressid, remaining the typical fair inconstant that he found in Benoît, falls as readily into the arms of her first lover as into those of her second. Chaucer’s Cressid is the first great character of English fiction. The characterization, delicate enough to keep her graciousness even in ruin, and to give the unashamed materialism of Pandarus engaging frankness and humor, is dynamic. It gives the story motive. Cressid is always dominant, not in having more space, but in bringing about before our eyes alike the heartbreak of Troilus and her own degradation. This is Chaucer’s achievement of narrative progress. Cressid, we say to ourselves, _would_ yield to Diomed. But though dominated by Cressid, the movement is of all three characters interacting, of characterization advancing by stages.[32] Thus Chaucer’s refocusing is neither modification of Boccaccio’s story nor such variation as had been already achieved; it is progressive motivation toward a significant issue. 3. Criticism of the _Poetriæ_ The dramatic interaction effective in _Troilus and Criseyde_ is less continuous, though no less striking, in the Canterbury interludes. It is not drama, it remains subordinate to narrative, partly because the time for drama was not ripe, more because Chaucer knew verse narrative for his own art. The bent of his genius he followed in both experiment and study. One of his first technical achievements, the weaving of description into the action, appears not only in progressive mastery, but also as distinct theory. Here evidently he discerned as a critic the deviation and the insufficiency of the poetic that he had learned at school.[33]