Blank verse poems make up nearly two-thirds of the poems in the history of English poetry. This type of poetry does not rely on repeating sound patterns, such as rhyming, but relies instead upon the rhythm of its syllables in relation to groupings of stressed and unstressed syllables. Using the natural stresses of words, a poet can build into a blank verse poetry line a rhythm that repeats in each line or uses variations of that rhythm throughout the lines of the poem. The most common form used in blank verse is known as iambic pentameter, the form used regularly by Edna St. Vincent Millay, John Donne, and William Shakespeare.
The different types of blank verse poems vary based on the prevailing traditions of blank verse schools around the globe throughout history. The types depend also on how these rhythm formulations have been used and varied by succeeding generations of poets. For instance, iambic pentameter is made up of lines that include five beats to each line, meaning five stressed syllables alternating with five unstressed syllables within a line. This would create a rhythm line of di-dum, di-dum, di-dum, di-dum, di-dum, with the "dum" being the stressed syllable and the "di" being the unstressed symbol. An example of that rhythm structure in a line of blank verse would be "The winds that swelled the clouds with tears o'erhead."
Ancient Latin poetry created blank verse rhythms alternating long and short syllables of ten syllables per line. The Old French school of blank verse used ten syllables, usually pausing at the fourth syllable, followed by one more ending unstressed syllable, making lines of 11 syllables. Some of the Italian poets, including Dante, used this 11 syllable form, stressing fourth or fifth syllables rather than pausing, however, as most Italian words have unstressed ending syllables. William Shakespeare used iambic pentameter blank verse in his plays. The English poets that used iambic or variations included William Cowper and John Keats; Irish poet William Butler Yeats and American poet Wallace Stevens used iambic blank verse poems as their preferred form.
Though iambic pentameter with its five beats of di-dum is most prevalent in blank verse poems, other forms include trochee with a dum-di pattern, anapest with a di-di-dum pattern, and dactyl with a dum-di-di pattern. Any combination of these rhythm patterns or variations upon them can be used in blank verse. For instance, sometimes a line may use what is known as double iamb where there are four syllables — di-di-dum-dum — that comprise two of the five feet in a line. Another instance would be a trochee tetrameter followed by what is called a tailless trochee: dum-di, dum-di, dum-di, dum.