If this be error and upon me proved, I never writ, nor no man ever loved.
The final two lines of the sonnet provide a dramatic and quite bold closing statement.
Line 13 uses rather legalistic language to basically say, "If these ideas are wrong and anyone can prove that I’m incorrect…"
The line poses something of a challenge to readers (do any of you have proof that he’s wrong?).
The final line resolves this challenge through a somewhat complicated twist; by saying that the poet has never written anything and that nobody has ever really been in love before if love actually turns out to be less than eternal, the poem’s truth immediately becomes impossible to dispute.
Why? Well, of course the poet has written – we’re reading his poem right now – and of course people have loved before…therefore, the ideas posed in the poem must be correct.
It’s odd logic, but hey, it works. Kind of. Just don’t think about it too much.