 The changing rhymes emphasize the dualist nature of beauty (how those things which are beautiful in their prime inevitably grow old, fade, and die), while the alternating pattern provides continuity.The independently rhymed couplet introduces yet another shift in the poem; the speaker reiterates how his beautiful beloved will be eternally preserved as long as men can breathe and see, and as long as the poem exists the beloved does, too.The term sonnet sequence might be rephrased as series or cycle of sonnets.