Most love poems lie a little. Swift's birthday poem for Stella begins by doing the opposite: it tells a woman, politely but plainly, that she is older and bigger than she used to be, and then asks her not to mind. The date in the title, March 13, 1719, marks the occasion, and the opening couplet sets a tone of teasing intimacy: "Stella this day is thirty-four, / (We shan't dispute a year or more:)". The parenthesis works like a wink. The speaker hints that the stated age may be a little off, and he is too gallant, or too sly, to haggle over it.
The central idea is that his admiration survives, and even grows, as its object changes. Since he first saw her "at sixteen," "the brightest virgin on the green," her "size and years are doubled." The arithmetic nearly works, since sixteen doubled is thirty-two, and the "year or more" covers the gap. The comfort comes in the pair of lines that follow: "So little is thy form declin'd; / Made up so largely in thy mind." Here "little" and "largely" push against each other, and the second line quietly puns on size. Whatever her body has gained, her mind has more than matched. A physical fact that most poets would hide becomes the basis of the compliment.
The second stanza turns that compliment into a fantasy. Suppose the gods could "split / Thy beauty, size, and years, and wit." Even divided, she would give the world two women better than any pair "so graceful, wise, and fair." The logic is delightfully backwards, because subtraction ends up as multiplication. The word "half" is repeated ("half the lustre of your eyes, / With half your wit, your years, and size"), and each half is still more than enough. Then the joke turns on the speaker himself. If Fate splits Stella, it must also "split my worship too in twain," so that "either nymph might have her swain." His devotion is so complete that the only way to love both halves properly is to become two lovers. The stanza opens with "split" and closes with "twain," which gives the fantasy a neat frame. The phrase "before it grew too late" adds a faint note of time pressing, a hint of mortality under the joking, though that is an inference from the wording.
The form keeps all this light. The lines are short, eight-syllable iambic couplets that move quickly and click shut on their rhymes: "four / more," "sixteen / green." Some of the rhymes are jokes in themselves. "Troubled / doubled" is a two-syllable rhyme that bounces comically, and "split / wit" and "Fate / late" make their points just by landing together. The second stanza runs to ten lines against the first stanza's eight, and the extra length feels like the fantasy running on past its natural stopping point.
The diction creates a second kind of comedy. Swift borrows the stock vocabulary of pastoral love poetry, with its "nymphs," "swain," "gods," "green" and "thy," and sets it beside the blunt word "size," which appears twice and is slipped into the list "beauty, size, and years, and wit" as if it were no more awkward than the others. The formal costume and the plain fact make each other funnier, and the plainness is what makes the praise believable. A compliment from someone who admits she has aged and grown is harder to dismiss than one that pretends she hasn't.
That is the poem's real achievement. It argues for Stella's wit by displaying wit itself, in the puns, the arithmetic and the neat reversal at the end. Readers who know Swift as the author of *Gulliver's Travels* may expect his sharp eye for the body to be cruel. Here it is affectionate. The poem looks at ageing directly, says what it sees, and turns the result into tenderness without flinching.