Everyone knows the opening line. Fewer people notice that Sonnet 18 quietly stops being about the beloved halfway through, and becomes a poem about its own survival.
The turn
The first eight lines admit a problem: a summer's day is lovely but temporary, and so is the young person being praised. "Every fair from fair sometime declines." Then comes the volta — the turn — at line nine: But thy eternal summer shall not fade. How? Not through love, or memory, but through the poem: So long lives this, and this gives life to thee.
A promise that came true
Shakespeare's claim is astonishing when you say it plainly: as long as people can read, he writes, this poem will keep you alive. It's a bet on his own words outlasting flesh. He made that bet around 1600. Four centuries later, a stranger on the other side of the world is reading about a person whose name we don't even know — and the promise holds.
Wear it
Our Sonnet 18 tee carries the opening line with the complete sonnet on the back. A love poem that's really about the thing you're wearing: words that don't die.