Before we get into nitty-gritty details, though, if you wanna read over the Shmoop take on all things ballad, head over here. We've got you covered.
Back already? Okay, here we go: here's where things get tricky. The poem is in pretty solid iambs, which means that every other syllable is accented. An iamb is a two-syllable pair where the stress falls on the second syllable: daDUM. Say "allow" to yourself out loud, and you'll hear an iamb. You'll also hear them here:
My candle burns.
And it's got lines that have an ABAB rhyme scheme. (The letters represent the end rhyme sound for each line, so line 1 rhymes with line 3, line 2 with line 4.) But here's the kicker: the first line doesn't have eight syllables. Gasp. It's got… seven:
My candle burns at both ends.
See what we mean? So how can we even call this a ballad?
Don't worry; we're not trying to pull a fast one on you. Millay's actually playing with the form of a normal ballad verse to make the first line shorter and punchier. It throws you just a little bit off guard, catching you off balance before you even get a chance to realize that there's supposed to be a solid rhythm to the poem's lines. And then, before you know it, you're back into a regular six-syllable and eight-syllable configuration. The poem slips smoothly back into a very, very traditional ballad meter, which might just be one of the oldest and most traditional of metrical patterns.
So why the upset in the first line? Well, we're guessing that Millay wants the reader to feel a bit on edge. After all, if you're in the presence of an all-consuming light, isn't it natural that things would be slightly non-normal? And coupling metrical irregularity with the announcement of an irregular, burning-at-both-ends candle is one good way to go about introducing abnormality.
This is a pretty unusual ballad, as ballads go. It's short. Super-short. Ballads are never short. So why combine traditional form with an untraditional length? Well, one way to make the new seem even newer is to refashion the old. And that's exactly what this poem does, appropriating the ballad into a short, snappy, new lyric.