A couplet concludes the sonnet by giving a solution to the quatrains. Keats accepts the unavoidable death; as a result, fears start to fade away. The poem is iambic pentameter, "When I have fears that I may cease to be," (1) which lets the poem have the smooth sound like the way people talk; thus, the rhythm of the poem makes the readers feel the poem is reserved, reticence, and calm. .
Talking about the structure of the poem, "Why did I laugh to-night," is also a traditional Shakespeare sonnet and has rhyme ABABCDCDEFEFGG. The poem consists of three quatrains and a couplet. Each quatrain has the same questions "Why did I laugh?" Asking, "Why did I laugh to-night?" (1), the poet responds " No voice will tell," (1). This shows that the poet asks questions, but he already knows that no body knows the answer. The poet asks second time "why did I laugh?" (6). This tells he does not receive the answer but he feels strong negative emotions, "O mortal pain!/ O darkness! Darkness! Ever must I moan," (6, 7). He asks the third time "Why did I laugh?" (9), then he responds to himself that "I know this Being's lease, (9). This shows he finally finds his impending death. A couplet concludes three quatrains. The conclusion is that the poet realizes death goes far beyond poems, fame, and beauty. In addition, the poem uses both iambic pentameter, "My fancy to its utmost blisses spreads," (10) which brings natural sound and trochaic pentameter, "O Darkness! Darkness! Ever must I moan," (7) which changes the rhythm of the poem to more powerful and scornful tone. .
In "When I have fears that I may cease to be," the tone of the voice is fearful, impatient, solitary, sorrowful, longing, depressing and despairing. Moreover, Keats uses syntax, "then on the shore / Of the wide world I stand alone," (12, 13) to emphasize the extensively huge shore where Keats stands alone. On the other hand, In "Why did I laugh to-night", the tone of voice is powerful, despairing, disappointed, anguished, bitter, solitary, conflicted, complex, doubtful, cynical, calm, confident, and hopeful.