In everyday speech, the emphasis of certain syllables can cause sentences to have a metered lilt. A poet will often use these syllables to make our language metrical and musical.
Just as we measure distance in inches, we have a unit of measurement for meter in poems. The smallest unit is known as a metrical foot. One of the most common types of metrical feet is the iamb.
An iamb occurs whenever a non-emphasized syllable is followed by an emphasized one:
The following words are all natural iambs: escape, agree, deny, attempt, compare.
However, in English, it is far more common to see iambs broken up between two words rather than to see a natural iamb in one word. For example, a poet is more likely to write iambs such as
to SWELL the GOURD, and PLUMP the HA-zel SHELLS (John Keats, from To Autumn)
rather than use a series of natural iambs.
In poetry, iambs are often grouped in lines of three (trimester), five (pentameter), or seven (heptameter).
Iambic trimester, in which each line would consist of three iambs (da-DUM, da-DUM, da-DUM) is most often seen in classical Greek tragedies and comedies, which were written for and performed at religious festivals in the ancient world.
Iambic pentameter is much more commonly seen in traditional English literature, from Shakespeare to Byron to the modern poets.
“Around the rocks, the rugged rascal ran.”
The previous line is a perfect example of iambic pentameter. Note how the five iambs are grouped together, de-emphasized syllables preceding stronger ones:
a-ROUND the ROCKS the RUG-ged RAS-cal RAN.
da-DUM, da-DUM, da-DUM, da-DUM, da-DUM.
You can also notice iambic pentameter in the works of Shakespeare:
shall I com-PARE thee TO a SUM-mer’s DAY?
And even the American Declaration of Independence:
we HOLD these TRUTHS to BE self-EV-i-DENT
Iambic heptameter can be seen in many poems, such as the light American classic Casey at Bat by Ernest Lawrence Thayer:
It looked extremely rocky for the Mudville nine that day.
You can count the seven iambs in the line:
it LOOKED ex-TREME-ly ROCK-y FOR the MUD-ville NINE that DAY.
This meter is also often used for ballads and other musical or story-telling devices.
You don’t have to stick to grouping your iambs in threes, fives, or sevens; any number of iambs per line is generally acceptable. When writing iambic verse, it is important to remember that variation is not wrong or a mistake. Not each set of syllables needs to be an iamb, and not every line needs to have exactly ten syllables. In fact, it has been argued that the successful manipulation of iambs and variations requires more skill than sticking to iambic verse alone.