The tone in Thanatopsis reflects the narrator's attitude toward the topic. Tone is made more intricate because the narrator ceases to speak for himself and begins to speak for Nature ("Comes a still voice--"). There are many mood shifts as the speaker in Thanatopsis shifts and as the discussion shifts. Overall, the ultimate tone would be drawn from the final set-off stanza ("So live, that when thy summons comes to join"), which represents the last tone shift, and would be summed up as soothing, comforting and uplifting, though the major portion is in Nature's voice and is illuminating and factual.
Prior tones, at previous tonal shifts, are casual and informing ("To him who in the love of Nature holds"); sad and eerie ("...and she glides / Into his darker musings,"); illuminating and factual ("Go forth under the open sky,"); somber ("...yet the dead are there:"); sad but factual ("...and what if thou withdraw / In silence..."); hauntingly final ("As the long train / Of ages glide away,"); soothing and uplifting ("So live, that when thy summons comes to join").
Tone is defined as the speaker's or narrator's voice (or tone of voice). The tone establishes the emotional intent of the poet or author and is delivered by the speaker or narrator and produces the emotional quality of the poem or narrative. Tone differs from mood because tone is conveyed through language alone while mood is conveyed through setting, objects, images, details and words.
The tone is surprisingly upbeat for a poem written by someone who has just been given a diagnosis of a disease that will cause death. William Cullen Bryant wrote the poem when he was in his late teens, having just received a mistaken diagnosis of consumption or Tuberculosis (T.B.) This disease caused inflammation and disease of the lungs that were eventually so much consumed that the patient could not breathe.
However, with the typical optimistic tone of the young, Cullen Bryant goes on to find comfort in the thought of his body 'going back to Nature' and becoming one with the trees and earth again. He comforts others in fatal circumstances by reminding readers of the great consolation that is to be found in Nature and his words have a comforting ring to them.Look also for areas in the poem where the tone seems to have the ring of resignation and acceptance to it. It has often been noted that the young have a more risk-taking and philosophical tone of thought towards their future life - and death.