the subject and the verb. The reader is left with confusion at the end of the line as to where the sentence is headed, or what the speaker is trying to convey. The second line is an example of less severe enjambment because it ends before a dependent clause; “Love is not love” could stand on its own as a full sentence, so the line break here is not as jarring as the first line break. Still, the line is not punctuated, and the reader must continue on for a deeper explanation of the poem's meaning.

The last two lines employ a paradoxical conceit. If there is no such thing as true love, the poet says that neither has he ever written, nor has anyone ever experienced true love. However, because the poem has been written, it means the poet, ultimately, is right about true love.
The effect is so much stronger in the latter than simply saying that love lasts.
To say it "is not love that alters" gets cuts to the heart of the reader's fear that love might change or end. "Love lasts," is too easy to say and it doesn't assuage any of that fear. It's like saying "I want to be with you," versus saying "I don't want to be with anyone else." They seem the same, but the former doesn't necessarily exclude wanting to be with another - maybe I just want to be with you, too. But the latter, is more powerful. It implies that I want to be with you, while also eliminating the possibility of there being anyone else.
The sonnet reminded me of the scripture passage in I Corinthians chapter 13 that goes over all that love is and isn't. The "love is patient, love is kind" passage that kids learn in Sunday school. I had never noticed before how often love is defined by what it is not. Verses 4-8, "[Love] does not envy, it does not boast, it is not proud. It is not rude, it is not self-seeking, it is not easily angered, it keeps no record of wrongs. Love does not delight in evil but rejoices