What "iambic pentameter" means in poetry

A term you'll meet in poetic meter.

Iambic pentameter is the most important meter in English poetry. Shakespeare's plays, Milton's epics, almost every sonnet you have read, and most serious English poetry through the 19th century are written in it. Understanding it gives you access to a huge swath of literature you would otherwise just float over.

The mechanics

An iamb is a metrical foot of two syllables: one unstressed, one stressed. Da-DUM. Pentameter means five feet per line.

So a line of iambic pentameter has ten syllables, alternating unstressed and stressed: da-DUM, da-DUM, da-DUM, da-DUM, da-DUM.

Shakespeare's "Shall I com-pare thee to a sum-mer's day?" gives you the basic shape. Five iambs, ten syllables, end on a stress.

Why English likes it

English is a stress-timed language. Our ordinary speech naturally clumps into iambic shapes — "be-cause," "a-lone," "to-day" are all iambs. A line of iambic pentameter sounds like elevated speech rather than song, because it is built from the same rhythms our mouths already use.

Ten syllables also happens to be roughly the longest unit a speaker can comfortably deliver in a single breath. That is one reason iambic pentameter has stayed the default for English dramatic verse for four hundred years.

Variation

Strict alternation gets monotonous fast. The mature pentameter line uses regular variations:

Trochaic substitution. Replacing an iamb with a trochee (DUM-da) — usually at the start of a line. "To be, or not to be" opens with a trochee.
Spondaic substitution. Replacing an iamb with a spondee (DUM-DUM) — two stresses in a row. Heavier, slower lines.
Pyrrhic substitution. Replacing an iamb with a pyrrhus (da-da) — two unstressed syllables. Lighter, faster.
Feminine endings. An extra unstressed syllable at line's end. "To be or not to be: that is the ques-tion" — eleven syllables, the last unstressed.

How to scan a line

Read the line aloud naturally. Don't force the meter.
Mark which syllables you actually stress.
Compare your stress pattern to strict iambs. Where does it vary?
Ask why the variation might be there. The meter breaks are usually expressive — emphasizing a key word, slowing a key moment.

Iambic pentameter and blank verse

Iambic pentameter is a meter; blank verse is a form — unrhymed iambic pentameter. Most of Shakespeare's plays, Milton's Paradise Lost, and Wordsworth's Prelude are in blank verse. Sonnets are in rhymed iambic pentameter and so are many longer poems through the 19th century.

How to read it

When a critic notes that a passage is in iambic pentameter, the useful question is not "is it iambic pentameter?" (most serious English verse is). The useful question is where does the meter break? The departures from the strict pattern are where the poet is doing expressive work — pointing emphasis, signaling emotional disturbance, or showing speech under pressure. Read for the variations, not the rule.

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