Hughes wrote “Harlem” in free verse, which means that the poem has no consistent meter. Notably, the only line in the poem with a standard metrical form is the first line: 

     What hap- | pens to | a dream | de-ferred?

This line is written in iambic tetrameter, meaning that the line consists of four iambs. (Recall that an iamb is a metrical foot with one unstressed syllable followed by a stressed syllable.) By opening the poem with such a readily identifiable meter, Hughes sets up an expectation for metrical regularity. Hughes then immediately thwarts that expectation by indenting the subsequent lines and avoiding rhythmic consistency for the rest of the poem. The jarring shift from iambic rhythm to a much less orderly meter echoes the speaker’s evident concern that the deferral of a dream leads toward degeneration and, possibly, to complete breakdown. Hughes further emphasizes the sense of increasing discontinuity by using end-stopped lines to break up the rhythm (lines 4–8):

     Or fester like a sore—
     And then run?
     Does it stink like rotten meat?
     Or crust and sugar over—
     like a syrupy sweet?

Note how the long dashes at the end of the first and fourth lines create a sudden, unnatural break in the middle of the rhetorical question being asked. These broken rhythms amplify the speaker’s sense that conditions in Harlem are degenerating.