In addition to metaphor, Langston Hughes uses repetition, imperative sentences, and imagery in his poem to make the point that having dreams or aspirations about a better future is central to a productive life.
Repetition creates a sense of rhythm and helps us remember a poet's words. Hughes repeats the same beginning phrases in the first three lines in both stanzas. This creates something very similar to anaphora, a literary device in which the same beginning words are repeated in consecutive lines. Both stanzas one and two contain the words "hold fast to dreams," "for," and "life is," creating a parallel structure.
In this poem, the speaker is giving suggestions or commands, likely to the reader; thus, the two stanzas contain imperative sentences. Because readers feel that Hughes is speaking directly to them, they are more likely to pay attention to his words and to imagine what they might feel like without dreams or aspirations.
Finally, Hughes uses imagery to create an emotional response. Imagery is description that uses any of the five senses of sight, sound, taste, touch, or smell. In stanza 1, Hughes evokes the image of a bird with a broken wing that cannot fly to convey the sadness of not having dreams. In stanza 2, he likens giving up on dreams to a field frozen with snow. This is a bleak, cold image that communicates the deathlike feeling of not having aspirations.