The tone and meaning of William Shakespeare’s sonnet 130 (“My mistress’s eyes are nothing like the sun”) are open to interpretation, as is especially the case with almost anything written by Shakespeare. However, the main purpose of this sonnet seems to be to mock other poets and sonnet-writers who offer exaggerated praise of the women they claim to love. The speaker in Shakespeare’s poem, in other words, is probably not making any great fun of his mistress, except in a gently teasing way; instead, he is making fun of the way other writers praise women.
Throughout most of the poem, the speaker lists some of the standard features that most poets mentioned when praising their mistresses, such as eyes, lips, breasts, hair, complexion, breath, sound of speech, and manner of walking. Shakespeare’s speaker calls attention to the hyperbolic, artificial, and literally unbelievable nature of much of this praise. By rejecting the conventional phrasing of other writers, Shakespeare’s speaker implies that his praise is more honest, more reliable, and more credible than theirs. By rejecting the kind of exaggerated phrasing used by other poets, Shakespeare’s speaker presents himself as a blunt, trustworthy, plain-speaking fellow. He also shows that he has a good sense of humor.
It’s important to note that the poem is not addressed to the mistress; instead, it speaks about the mistress. If it were addressed to her, it might sound a bit insulting. However, because the poem is written about her, it functions mainly as a kind of joke at the expense of other poets.
The final lines of the work are especially intriguing:
. . . by heaven, I think my love as rare
As any she belied with false compare. (13-14)
On the one hand, the speaker here seems to offer his mistress high praise by calling her “rare” (that is, admirable, extraordinary); on the other hand, he concludes by saying that she is as admirable as any woman who is praised in exaggerated and unreliable ways. Thus, the poem concludes on a note of ambiguity and ambivalence. Ultimately the speaker merely seems to claim that his mistress is at least as attractive as any other woman. This is not the kind of hyperbole most mistresses or readers would have come to expect, but at least it is honest, and playful honesty seems to be the chief tone of this poem.
Shakespeare's Sonnet 130 is sometimes taken to be an anti-sonnet, truthful and accurate in depicting the so-called "Dark Lady" of the sonnets. This is more likely, I think, an attempt to wryly parody most sonnet sequences, including Shakespeare's own, but when we get to the couplet, Shakespeare brings us back to the standard Petrarchan ending--his love interest is as incomparable as "any she belied" with the standard false comparisons that litter the average sonnet.
Admittedly, the picture Shakespears paints of his lady is grim--her breasts are dun colored (a dull grayish tan color), her hairs are black wires (perhaps an allusion to Medusa's head of snakes), her breath "reeks" (but he qualifies that by saying that only "some" perfumes are better than his lady's breath). In addition, she is clearly not to be compared to a goddess, who glides above the ground, because Shakespeare's lady "treads" just like the rest of us.
I think it's clear that Shakespeare decided to poke fun at the traditional, conventional Petrarchan sonnet that aggressively sought to compare ladies to natural objects that they couldn't possibly be truly comparable to and to remind other sonneteers that their ladies are are actually much more mundane than they are made out to be even by the most skilled and imaginative poet.
The couplet, however, moves us back into the realm of conventional sonnet beauty when Shakespeare admits that his lady is as truly beautiful as any lady whose beauty is described with the usual idealistic comparables.