What is iambic pentameter, and why is it the most popular metre in English poetry? There are two things which need to be addressed here: what ‘iambic’ means and what ‘pentameter’ means. So, by way of introduction to this common metre, here’s a little bit of background on iambic pentameter – with some examples of how it’s been used by some of the greatest poets in the English language.

Lines of poetry can be counted in terms of syllables. So, in this line from Shakespeare’s Romeo and Juliet:

But soft! what light through yonder window breaks?

We can count the syllables in the line and conclude there are ten syllables in it. There are six monosyllabic words and two disyllabic ones (‘yonder’ and ‘window’). But we can also talk about how those syllables are put together to form a rhythm or pattern. After all, we don’t pronounce every single syllable with the same amount of emphasis or stress: some syllables carry a lighter stress, others a heavier stress.

In the word ‘window’, for instance, we place more emphasis or stress on the first syllable than the second: we say ‘WIN-dow’, in other words, rather than ‘win-DOW’ (or ‘WIN-DOW’). The same with ‘YON-der’: the main stress is on the first syllable of the word.

Identifying iambic pentameter

If you were asked to emphasise those syllables in Shakespeare’s line which have a heavier stress, it would look something like this:

But SOFT! what LIGHT through YON-der WIN-dow BREAKS?

So what we have is a recognisable pattern where the syllables alternate between light stresses and heavy stresses. In short, we have a set of pairs of syllables: one lightly stressed, followed by one heavily stressed; then another lightly stressed, followed by a heavily stressed one; and so on. We can show these pairings as follows:

But SOFT! / what LIGHT / through YON / der WIN / dow BREAKS?

The technical name given to a poem’s rhythm, or rather the ground-plan for its rhythm, is metre. The technical name for the analysis of a poem’s metre is scansion, but we don’t need to concern ourselves with that bit right now. There are different kinds of metre, based on the kind of foot the poet is using: ‘foot’ being the technical name for the units of the poem’s metre.

The name for a foot where we have a light stress followed by a heavy stress is an iamb. (A good way of remembering this is to think of an iamb as being ‘the great I AM’ – although the word itself is pronounced ‘EYE-am’, think of it as ‘eye-AM’, so that you remember that an iamb is a light stress followed by a heavy one.)

So, to return to that line from Shakespeare, we can see that

But SOFT! / what LIGHT / through YON / der WIN / dow BREAKS?

is a line of iambic metre. But we can be a bit more specific than that: there are five feet – five iambs – in that single line of verse, as the divisions between each foot shows. So we can say this isn’t just iambic metre: it’s iambic pentameter. If the line was shorter (‘What light through yonder window breaks?’, for instance), we could say it had four feet, four iambs, and so it would be an example of iambic tetrameter, with ‘tetra-’ meaning ‘four’.

Iambic pentameter has been in English poetry for a long time, since at least the work of Geoffrey Chaucer in the fourteenth century. It is the metre found in blank verse – what most of Shakespeare’s plays are written in (indeed, Shakespeare’s sonnets are also written in iambic pentameter, with the exception of one).

Uses of iambic pentameter

It is the metre of the heroic couplets used by Alexander Pope and John Dryden. It is everywhere in Paradise Lost. It’s integral to many of Browning’s and Tennyson’s dramatic monologues. Why has iambic pentameter proved such a usable and versatile metre for English poetry?

Well, the reason often given is that iambic pentameter is the metre which most closely approximates to natural human speech in English. Many of our words are iambic; many of our sentences fall naturally into an iambic rhythm. And five feet – ten syllables – is not a bad approximation for the length of a clause in English. And sometimes you can speak in iambs when you hadn’t even thought to speak in verse. As in that last sentence. Did you hear the iambic pentameter?

And SOME-times YOU can SPEAK in I-ambs WHEN
You HAD-n’t E-ven THOUGHT to SPEAK in VERSE.

This sort of thing happens far more often than we find ourselves lapsing naturally into trochaic tetrameter, for instance (but that’s a metre for another day).

Of course, iambic pentameter as a term tells us nothing about whether the lines of poetry written in it are rhymed or not: blank verse is unrhymed iambic pentameter, while heroic couplets are iambic pentameter verse lines rhymed aabbcc, and so on. In addition to this, lines of iambic pentameter might be end-stopped or they might be run-on lines.

End-stopped lines

End-stopped lines of iambic pentameter can be especially useful when writing didactic verse – poetry designed to instruct, or to impart a moral message – as Alexander Pope showed in his 1711 poem An Essay on Criticism:

True ease in writing comes from art, not chance,
As those move easiest who have learn’d to dance.
’Tis not enough no harshness gives offence,
The sound must seem an echo to the sense.
Soft is the strain when Zephyr gently blows,
And the smooth stream in smoother numbers flows;
But when loud surges lash the sounding shore,
The hoarse, rough verse should like the torrent roar.

Pope’s lines of iambic pentameter are end-stopped because each line concludes with a pause, signalled by a mark of punctuation: a comma, a semi-colon, a full stop. This has the effect of rendering each line its own little unit, allowing us to pause for breath once we reach the end of each line, take in the point being made, and then continue.

(Pope is also writing in heroic couplets – pairs of iambic pentameter lines rhymed aabbcc and so on – so each couplet forms its own self-contained point. If you look at the end of every even line above, you’ll see it concludes either with a full stop or a semi-colon, which is a sort of ‘light’ version of a full-stop, a halfway house between the comma and full stop.)

Contrast Pope’s end-stopped lines of iambic pentameter with these lines, written at the other end of the eighteenth century by William Wordsworth, in his poem ‘Tintern Abbey’ from 1798:

Five years have past; five summers, with the length
Of five long winters! and again I hear
These waters, rolling from their mountain-springs
With a soft inland murmur.—Once again
Do I behold these steep and lofty cliffs,
That on a wild secluded scene impress
Thoughts of more deep seclusion; and connect
The landscape with the quiet of the sky.

These lines, like Pope’s, are written in iambic pentameter, but there are two crucial differences. First, they’re unrhymed. Second, Wordsworth’s lines aren’t end-stopped. Instead, we get treated to a series of run-on lines (the French term sometimes used for this is enjambement), whereby the end of each line moves seamlessly into the beginning of the next.

So at the end of the second line (‘again I hear’), we have to keep reading onto the next line to find out what Wordsworth heard (‘These waters’). We can observe a key difference between these two uses of iambic pentameter: Pope was going for the pithy, artificial, controlled line for rhetorical effect (rhyming couplets; end-stopped lines), whereas Wordsworth almost wants us to forget his lines are written in iambic pentameter at all (no rhyme; run-on lines).

But of course, Wordsworth’s lines are just as much iambic pentameter as Pope’s. And both Pope’s and Wordsworth’s iambic pentameter verse does exploit that chief quality that iambic pentameter possesses: its similarity to the rhythms of English speech.

With Pope, it’s as if he’s declaiming from a pulpit or lectern (his poem is called An Essay on Criticism, after all), but with Wordsworth, it’s more like someone taking us into their confidence and talking quietly to us about their memories and experiences. With both examples of iambic pentameter, we can begin so see why this metre has been so useful to so many poets over the centuries.