Tone is generally determined by several factors. In Langston Hughes's poem "Harlem," tone can best be determined by his use of imagery. This work has a simple structure: it is a series of images which draw a picture of the answer to a question he asks but never answers: "What happens to a dream deferred?" The images that follow are possible answers to that question and full of sensory details which lead to a feeling of hopelessness.
Does it dry up
like a raisin in the sun?
Here we have the visual and tactile image of something once full and ripe which is now shriveled and dried up--like a dream deferred.
Or fester like a sore—
And then run?
This image is one of a partially crusted but mostly open sore which has not healed; instead, it oozes its ugly fluids and never really heals--like a dream deferred.
Does it stink like rotten meat?
The image here is one of a life-giving substance which is now inedible and has the look and smell of decay--like a dream deferred.
Or crust and sugar over—
like a syrupy sweet?
Here I think of something like maple syrup left to dry up on a plate--hard and crusty and no longer smooth and usable--like a dream deferred.
Maybe it just sags
like a heavy load.
This image is one of pure weight, a burden which will not be lifted. Visually, the word "sag" depicts an utter hopelessness--like a dream deferred.
Or does it explode?
Finally, all the senses are invoked in this image--sound and sight and touch and smell and even taste, as the smoke and dust of an explosion fills the mouth. There is nothing left; all is lost--like a dream deferred.
This structure of rhetorical questions replete with sensory images and details is designed to create a growing sense of hopelessness, which it seems to me is both the tone and the theme of this poem.
For tone, one might consider the pathos exhibited in the sorry plight of Chonita as she receives a scolding before being given food (paragraph 11). Here the technique is the narrator’s straightforward description, with no accompanying analysis or discussion. Dr. Zapata expresses indignation at Chonita’s death, and Paredes provides enough details for the doctor to substantiate his anger (paragraphs 21–33). That Dr. Zapata is a physician, thinker, and a caring person makes his anger credible. His declaration that he is not a political revolutionary is also consistent with his concern for the personal plight of persons like Chonita.