But thy eternal summer shall not fade, Nor lose possession of that fair thou ow’st,
The turn! Check out the "Form and Meter" section for more on line 9 in sonnets, but here’s a classic example of a "turn."
Suddenly (though it was foreshadowed a bit in line 8), the tone and direction of the poem changes dramatically. Moving on from bashing summer and the limitations inherent in nature, the speaker pronounces that the beloved he’s speaking to isn’t subject to all of these rules he’s laid out.
The speaker argues that, unlike the real summer, his beloved’s summer (by which he means beautiful, happy years) will never go away, nor will the beloved lose his/her beauty.
But remember what we mentioned in line 4? The summer in real life actually is an "eternal summer," since it comes back every year for all eternity. Just like we saw with all of the personifications of nature in the previous lines, we begin to notice here that "thee" and the "summer’s day" are really quite similar.
Both can fade away or, depending on how you look at it, be eternal, and both can be personified. That’s why here, at line 9, the poet switches direction – both the beloved and nature are threatened mainly by time, and it is only through this third force (poetry), that they can live on.
It’s also worth picking up on that word "ow’st." That apostrophe might be contracting "ownest" or "owest," and both work nicely. Either the beloved won’t lose the beauty he/she possesses ("owns"), or won’t have to return the beauty he/she borrowed from nature and now owes back.
These readings both resonate well with line 4, in which the speaker described the summer months as a "lease," or a temporary ownership that had to be returned.
Nor shall death brag thou wander’st in his shade, When in eternal lines to time thou grow’st;
In another bit of personification (so far we’ve had summer and the sun), the speaker introduces death.
Death, the speaker claims, won’t get a chance to claim the beloved in the valley of the shadow of death (this death’s shadow idea is from Psalm 23:4), since he/she is immortal.
The general meaning of line 12 (you’re eternal) is actually easier to see if you read the line as a metaphor. As a metaphor, "lines to time" definitely refers to a poem, since they are lines set to a meter, or time.
Here, then, the poet is making two bold claims: first, that his poem is "eternal," and second, that it nourishes and develops "thee," as it is where he/she is able to "grow."
Now this willingness to discuss the fact that he’s writing a poem within the poem itself is pretty cool stuff.
One fancy way of describing this kind of artistic tactic is called "breaking the fourth wall." That’s a metaphor itself, and you can think of it as a stage: in a normal play, any indoor action goes on as if the front edge of the stage were an imaginary wall. The actors, in other words, are supposed to pretend they’re in a real world with four walls and no audience watching them. If the actors, however, recognize that there’s an audience out there, they’re considered to be "breaking" through that fourth wall, as they try to do away with the artificiality of pretending they’re just living out a normal life up there on stage.
Well that’s exactly what’s starting to go on here. If you were thinking this poem was a love letter to a beloved, you can forget it. This is a poem written to be read by an audience, and that audience, by continuing to read the poem, will try to make the beloved grow into a character, and in turn make him/her immortal.
So long as men can breathe, or eyes can see, So long lives this, and this gives life to thee.
The couplet, in the end, is really just a fuller admission of what the speaker points toward in line 12.
He has completely shattered the fourth wall, and (successfully, we should add) predicted that this poem will continue to be read, and the beloved will continue to be analyzed and re-analyzed for all time.
In other words, by allowing us to try to give life to "thee" (figuring out who he/she was), the speaker and the poem itself give "thee" life.
In other words: as long as men live and can read, this poem will continue to live, and so keep "thee" alive.
But let's examine the language more closely. First of all, we’ve got some more personification: technically, eyes don’t really "see," and poems certainly don’t "live."
Also, it’s worth noting the incredible arrogance here: why should we believe that as long as humankind exists, this poem will continue to live? Can’t we imagine a world in which every copy of this poem were burned, and so "thee" would stop living?
And even if people are still reading the poem, what kind of "life" is it that the beloved will be leading? This definitely doesn’t sound like heaven. The beloved can’t make any choices for his or her self, isn’t conscious, and can only be recognized as the poet described him or her.
In fact, we ought to wonder whether it is "thee" who will be alive, or rather the poet’s (very limited) representation of "thee."
Plus, remember how in line 9 we noted that summer could also be eternal? Well, the end of this poem kind of makes you wonder. So why, again, is the beloved eternal but not summer? Just like summer, the beloved is going to fade away in real life, and just like summer, the beloved has been written about and preserved in a poem. How come, by the end of the poem, it’s only "thee" who lives on and not nature?
Finally, remember how back in line 1 we were already wondering if "thee" might not just be the speaker’s lover, but also us readers? Well now the speaker has broken through the fourth wall, and revealed himself as not just a lover, but also as a writer of poetry.
So check this out (this should be fun for you math kids out there): the speaker is talking to "thee," and that speaker is actually the poet. Now who do poets write for? That’s right, for us readers.
So we have three conditions here: the speaker speaks only to "thee," the writer speaks only to us, and the speaker and writer are the same thing. Doesn’t that mean, then, that "thee," is the same as "us"? Trippy.
Frankly, we think that’s a pretty cool reading. Basically, the speaker here is speaking to all of mankind. All of us feel this pressure of mortality, but here Shakespeare crystallizes that anxiety in a poem, so that this idea of mankind will live on forever.
The last lines, then, can be read as circular: "so long as mankind lives, mankind will continue to live."
Cool? Too weird? You decide.
In any case, these last two lines hammer home something we suspected from those very first pronouns: this speaker seems more interested in himself and his abilities as a poet than the qualities of his addressee.