Let me not to the marriage of true minds
Admit impediments; love is not love
Which alters when it alteration finds,
Or bends with the remover to remove.
O, no, it is an ever-fixèd mark
That looks on tempests and is never shaken;
It is the star to every wand'ring bark,
Whose worth's unknown, although his height be taken;
Love's not Time's fool, though rosy lips and cheeks
Within his bending sickle's compass come;
Love alters not with his brief hours and weeks,
But bears it out even to the edge of doom.
If this be error and upon me proved,
I never writ, nor no man ever loved.
All of Shakespeare's sonnets are somewhat mysterious; they were published without his involvement and were written under circumstances unknown to us. Much ingenuity has been expended over the centuries in trying to figure out the real identities of those involved and what exactly prompted the series. These efforts are mostly useless. Even a solid guess can't be verified at this late date. And it's unclear why the real identities and circumstances are (at this late date!) important to us, outside of idle though understandable and often well-meaning curiosity. The poems must stand as poems, and continue to engage readers or not on poetic grounds, and those include psychological grounds – you can analyze and argue over what the poet is saying and why he's saying it without getting too wrapped up in the particulars of whom, historically, he said it to and why – in short, you can analyze Shakespeare's sonnets the way you would analyze a speech in one of his plays.
This is by way of saying that I think this poem is a little stranger than it appears at first glance. Why is the poet arguing so vehemently about the true nature of love, and insisting that to be true it must be unchanging? I've always sensed a sort of rebuke implicit here – is he stepping aside for two people in love with each other, or insisting that he's the one who really knows what true love is? If you read the first line in regular iambic pentameter (that is, five beats of an unaccented syllable followed by an accented one, the usual rhythm for a sonnet), then there is an emphasis on me, as if he's speaking in ironic deprecation ("God forbid that I should be the one to come between you two, and my explanation will show you that I am the one who truly understands what love is.")
Admit impediments is probably a reference to the marriage ceremony in the Book of Common Prayer and annotated as such in the edition I used (for which see below): "If any of you know cause or just impediment. . . " But the reference here is not to a regular (legal, physical, setting-up-housekeeping) kind of marriage; it's to a higher emotional and spiritual state: a marriage, a union, of true minds. But what exactly does admit mean here? Does it signify let me not acknowledge or confess that such things can exist in the marriage of true minds (that is, if I allow that such things are there, then this does not qualify as a marriage of true minds)? Or does it mean let me not allow these things to enter into the marriage of true minds (that is, you can do or say what you want, but I refuse to let these things into the unchanging love that is a marriage of true minds)? Is the speaker a party to this true-minds marriage, or a (possibly partial) onlooker?
The poem is structured in the classic English (or, as it's also called, Shakespearean) sonnet style: three quatrains and a concluding couplet, to make up fourteen lines of iambic pentameter. (The other major style, the Italian or Spenserian sonnet, is divided into an octave and a sestet.) The first quatrain starts out with a hint of official language (the echo of the marriage service from the Book of Common Prayer), but the poet is quickly swept up in the balances, paradoxes, and word-play beloved of Elizabethan writers: love / not love, alters / alteration, remover / remove. (Is alter a pun to remind us of the altar at which an official marriage would take place?) But he states his case fairly clearly and cleanly: true love is unchanging. In the second quatrain, he steps up the rhetoric. O, no, as the quatrain starts sounds to me as if he is arguing with someone (even if it's himself). He compares unchanging love to the North Star (the ever-fixèd mark) whose unvarying position in the night skies guided sailors in their navigation (the star to every wand'ring bark – a bark, also spelled barque, being a type of sailing ship). The position of the North Star is known (his height [that is, its location in the sky, is] taken), and that is why its value is unknown, which in this context means something like something that can't be quantified, the way we say that something of great value is priceless (though perhaps there's also a suggestion there that its true value is unknown in the sense of being not realized or thought of – another hint that one of the lovers is heedless). In this quatrain, the poet has moved beyond his general statements on the nature of love to compare it to life-and-death situations (a tempest at sea) in the physical world.
The third quatrain heats up the rhetorical stakes still further, from the physical to the metaphysical, though in all three quatrains, the poet remains as unwavering in his position as Love itself: he is restating, not revising. In this quatrain, it is Time and Eternity that are the enemies of Love, not just tempests and creaking vessels: we are told that Love is not Time's Fool (fool in the sense of an entertainer, a plaything or possession, the licensed joker in an imperious monarch's court), though the beauties (rosy lips and cheeks) that might inspire love do fall victim to Time: but again, we are not talking about mere physical longing or lust, but about a union of true minds. True love moves beyond the body, as it must if it is to be constant (which, according to the poet, ir must by definition be): the body changes, love does not. Time is personified in the familiar way, as a figure with a sickle (the sharp and bending harvest tool with which we, like the grass, are cut down). Compass here means a circular sweep, but the word also hearkens back to Love as the North Star guiding mariners. Alters in this quatrain also is a reminder, this time of the first quatrain (that alters when it alteration finds). These insistent echoes reinforce the consistent message about the unchanging nature of Love.
When we reach the edge of doom with Love still unchanging, we have reached as far as we can go. Doom seems like a dreadful and fatalistic word to have here; more than just an end, even an apocalyptic end, it suggests destruction, fate, and the Day of Judgment (doomsday). Love survives and surpasses even the onslaught suggested by doom. Our poet has reached a fever pitch of emotion (or possibly hysteria). Having gone to the edges of the universe and Time, he concludes with what seems an oddly flat and formulaic couplet: If this be error and upon me proved, / I never writ, nor no man ever loved. (The rhyme proved / loved, like the earlier ones of love / remove and come / doom, would have been regular in Shakespeare's time.) The couplet at the end of this style of sonnet is usually a sort of summation or a final consolidating statement; this one sounds to me like the end of an affidavit, like the sort of legalese you'd use to sum up sworn testimony; proof is a legal term, and he's asking for proof of error – that is, I put this to the trial and dare you to convict me of error here. This echo of official language hearkens back to the use of the official marriage ceremony in the first two lines; though these lines might seem detached from the rest of the poem, they actually, through this echoing, remind us of its internal consistency. And they do so while continuing the argument in the only way possible after the poet has stated his position and expanded it to the physical and temporal worlds: they state that if what he has said is not true, then nothing is true: he has never written (and yet we've been reading what he's written), and no man was ever in love (and is not he in love? or at least describing the love he sees?)
I used the Signet Classic Shakespeare edition of The Sonnets, edited by William Burto. An additional appeal to this edition is the introduction by W H Auden. I hadn't read the intro in years so I glanced over the beginning and see that he starts the way I do, dismissing the attempts to identify the real people and events behind the sonnets. I am happy to be in agreement with Wystan. Opera fans will have recognized the influence of this sonnet in particular on the libretto for The Rake's Progress, which Auden and Chester Kallman wrote for Stravinsky. At the end of Act 1, when Ann Trulove decides to leave the country and search for Tom Rakewell in London (Love hears, Love knows / Love answers him across the silent miles, and goes) the cabaletta (the quick final section) of her aria is: I go to him. / Love cannot falter, / Cannot desert; / Though it be shunned / Or be forgotten, / Though it be hurt, / If love be love / It will not alter. / Though it be shunned / Or be forgotten, / Though it be hurt, / If love be love / It will not alter. / O should I see / My love in need / It shall not matter / What he may be. / I go to him. / Love cannot falter, / Cannot desert; / Time cannot alter / A loving heart, / An ever-loving heart. Again we have the use of alter, the repetition, the emphasis on the unchanging nature of true love, and the victory of love over Time. Sadly for Ann, hers is a case in which the unchanging truth of her love is one-sided, bestowed upon an unworthy object.