Lines 13-23 Summary

Lines 13-16

Being certain that they and I
But lived where motley is worn:
All changed, changed utterly:
A terrible beauty is born.

• Yeats was always certain that the social world where he talked to these people is a world "where motley is worn" (14). Motley refers to the patchwork of colors that would traditionally be worn by a jester or old-timey comedian. By associating a silly life with the kind of "motley" clothes people wear, Yeats is also using a little device called metonymy. Basically, he's playing on our usual associations with clown clothing to make us think of his entire social life as silly and pointless. 
• This is another image Yeats uses to say that he always assumed these people lived in a world where you went to work, joked around at the bar, and called it a day. 
• But now, something that has happened that has made "All changed, changed utterly" (15). Readers of Yeats back in the day would have known at this point that Yeats is now referring back to this poem's title, "Easter, 1916," which refers to a bloody uprising in Ireland's history. This uprising still would have been fresh in people's minds when Yeats published this poem in 1921. So readers here would definitely be waiting for Yeats to get to the part about people dying.
• Yeah, now we're getting somewhere as far as poetry goes. Now Yeats isn't all like, "I don't really care about talking to people on the street." Instead, he talks about a "terrible beauty." 
• Apart from the fact that both of these words are very different in tone from the rest of the first stanza, they also create a lot of conflict right off the bat by being an oxymoron. By definition, beauty is supposed to be a good thing. So what are we to make of a guy who refers to a certain type of beauty as "terrible?" That's a question that only reading the rest of the poem can answer. It's also a little technique called foreshadowing. Stay tuned.

Lines 17-20

That woman's days were spent
In ignorant good-will,
Her nights in argument
Until her voice grew shrill.

• It's not totally clear which woman Yeats is talking about here. But some quick research tells us that it's probably the Countess Constance Markievicz, who was one of the main people behind the Easter Uprising. She was sentenced to death, but got the sentence reduced to life in prison. 
• Here, Yeats isn't exactly showering praise on the woman who gave her life to the Irish cause. In fact, he says that much of the goodwill this woman showed was ignorant and uninformed. He also says that this woman liked to argue so much that her "voice grew shrill" (20). These aren't exactly kind remarks for someone who would've been a national hero in Ireland when Yeats was writing this. 
• By using the phrase, "her voice grew shrill," Yeats is also bringing us back to one of his favorite poetic techniques—metonymy.
• When he says that the woman's voice grew shrill in these lines, that's not all he actually means. What he's saying is that this woman's involvement in politics has taken away her feminine beauty, which Yeats symbolizes here through the idea of a once-beautiful voice getting shrill over time because its owner won't stop arguing about politics.

Lines 21-23

What voice more sweet than hers
When, young and beautiful,
She rode to harriers?

• In these lines, though, Yeats sounds like he's changed his tune. Suddenly, his tone seems nice when he asks what voice was sweeter than the Countess's when she was young and beautiful and "rode to harriers." This last phrase is a British phrase meaning that the woman rode on a horse during a hunt for rabbits. But when you think about it, it's kind of a nice symbol of rich beauty. Can't you just see the Countess riding on her horse through a beautiful green forest, birds chirping on every side of her? 
• But by using the metonymy of a "shrill voice" to show an ugly change, Yeats seems to be saying that the Countess was once a young and beautiful woman who did beautiful rich-people activities like rabbit hunting. But as she got older, she got involved in the dirty world of politics and her voice got shrill. Yeats here isn't exactly advocating for women to enter politics. It seems that he prefers them young, rich, beautiful, and away from the public sphere. Not the most forward-thinking message, but there you have it.