1600s: Men who wanted to gain the affection of their lovers would sing them lyrics written by poets like Jonson and Campion.

Today: Valentine's Day has made fortunes for companies like Hallmark, since the preferred token of affection has become a card, often containing a verse that expresses an artificial sentiment.

1600s: Love sonnets and songs had distinctive styles and forms that employed measured rhythm and rhyme schemes.

Today: Modern poetry is often characterized by its free verse and unregulated style.

1600s: While the Church of England was the dominant religious body in Britain, poets often evoked Greek and Roman gods in their poetry, as Jonson does when his speaker compares his lady's kisses to Jove's nectar.

Today: Most modern poetry is secular, or worldly, reflecting the gradual decline of the influence of religion on the arts. Religious groups, however, are becoming more politically...