(Not So) Heroic Couplets
Heroic couplets—sets of two lines of rhyming iambic pentameter each of which forms a distinct rhetorical as well as metrical unit—were hands-down the most popular poetic form in the later 17th and early 18th century in Britain.
Origins
The origins of heroic couplets are murky—they go back to at least Geoffrey Chaucer in the 14th century—but they first got their name in the 17th, where they were the main poetic form used for heroic drama. By the 1700s, almost every poet used them for almost every poem. But of all of those poets, Alexander Pope was the master of the heroic couplet. Lucky you: reading The Rape of the Lock is about as good a lesson as you could possibly get in the best way to write, and use, heroic couplets. (You can find a briefer lesson in our guide to part of Pope's later poem, An Essay on Criticism, called "Sound and Sense").
Breakdown
First, let's break them down into their component parts. Each line of heroic couplet is made up of five poetic feet, called iambs (that's Greek), which are units of two syllables: one unstressed, followed by one stressed.
Because there are five feet in each line, the lines are called pentameter (from "penta," or five—Greek again). Do the math: this means each line of each couplet will have ten syllables total. Take a look at the first couplet of The Rape of the Lock for an example:
What dire Offense from am'rous Causes springs,
What mighty Contests rise from trivial Things, (I.1–2)
Can you see how iambic pentameter is a good choice for long, narrative poems like this one? The rhythm of unstressed/stressed marches you forward at a steady pace: not too fast, not too slow. Ever run a marathon? Well, if you did, you'd know that a steady unchanging pace is what gets you to the end. Iambic pentameter lines are the marathon pace of poetry.
The rhymes, too, help us get where we're going: they set each couplet off as unit (as above, with "springs/Things"), and when that unit ends, we're already looking forward to the next rhyme, carried there by the steady march of the iambic pentameter.
Couplets and Comparisons
The fact that these are couplets makes them especially good for comparisons and contrasts—the juxtaposition we know Pope is so keen on throughout the poem.
Each line of the couplet can contain one thing—a person, a metaphor, an allusion— that contrasts with whatever is coming in the second line, as in Canto II when Ariel worries about what will happen to Belinda at the party:
Whether the Nymph shall break Diana's Law,
Or some frail China Jar receive a Flaw, (II. 105–106)
As we detailed in our "Summary" section, "Diana's Law" is the law of chastity, and Pope is here juxtaposing that very serious rule for young women, with the very next line's relatively trivial crack in a piece of decorative pottery.
Simultaneously, though, as the formal relation of these two lines tells us, he's also saying that Belinda's reputation is just as fragile as a china jar. The side-by-side placement of the lines underscores the side-by-side comparison/contrast of what the lines are about.
The juxtaposing power of heroic couplets doesn't stop at the level of the line, though. Given there are five metrical feet in each line—an uneven number—a crafty poet can insert pauses, or caesurae, within each line at strategic places.
A pause makes you slow down and consider what you've just read for a moment, and sets you up for the next part of the line. Pope does this here at the beginning of Canto III, when he describes Hampton Court and introduces us to the Queen:
Here Thou, Great Anna! Whom three Realms obey,
Dost sometimes Counsel take—and sometimes Tea. (III.7–8)
See the comma and the exclamation point in the first line of this couplet? Those are pauses, or caesurae, that set the Queen's name ("Great Anna") off from the other words in the line. Very respectful indeed.
Now look at the dash in the second line. It's another caesura, this time a long pause between the first three iambs of the line, and the last two. Those first three iambs are about some serious stuff: the "Counsel" the Queen takes with her ministers and advisors as she governs the realm. But what about the last two? Those are about the relatively trivial matter of taking tea.
We point out the relatively silly juxtaposition between these two things in our "Summary" of the poem. Here, do you see how well the form itself works with such juxtapositions? No wonder Pope found this form perfectly suited to what he was up to in The Rape of the Lock.