He uses the repetition of identical or similar vowel sounds; "Does it dry up like a raisin in the sun?". Up and sun do not rhyme, but they have the same "uh" sound.
Rhyme:
Poetry having correspondence in the terminal sounds of the lines. "Does it stink like rotten meat?...like a syrup sweet?" Meat and sweet rhyme. They have the same ending "eat" sound.
Alliteration:
The repetition of the same letter at the beginning of two or more words immediately succeeding each other, or at short intervals. For example, the "s" sound in syrupy and sweet is repeated. This adds emphasis to the phrase.
Imagery/Figurative language
Langston Hughes uses a lot of imagery in this poem. Imagery is a specific language that describes sensory details. This gives a very vivid picture of the ideas in the poem. Dream Deferred is almost all imagery. An example of that would be; "Or crust over like a syrupy sweet?"
This sentence portrays a picture in my mind of a old crusty hard candy lying in a gutter covered in mud.
Also, In the beginning of the poem, Hughes uses visual imaging/similes to compare a 'dream deferred' to a raisin. "Does it [the dream] dry up/Like a raisin in the sun?". The once raisin healthy looking grape, has shriveled up to become a raisin. The question remains, why compare a 'dream deferred' to a raisin? For one, the appearance of the raisin isn't emphasized, so the description isn't as significant as the simile. What Hughes is attempting to communicate is that like a raisin, a dream deferred shrivels up and turns dark because the sun has baked it (negative connotation). The comparison of the dream to a withered raisin emphasizes how a dream that is postponed changes dramatically and will not turn out as the person originally intended.
Connotations
For example,