Final answer:
A turn after the first two quatrains of a Shakespearean sonnet typically signifies a shift in tone or argument, known as the volta.
Step-by-step explanation:
The turn after the first two quatrains of a Shakespearean sonnet usually signifies a shift in tone or argument. In poetry, this turn is known as the volta, and it can indicate shifts in a poem's mode or voice, including between narrative and lyrical modes, or from descriptions to questions. In the specific structure of a Shakespearean sonnet, which consists of three quatrains followed by a couplet with the rhyme scheme abab cdcd efef gg, the volta often appears either after the eighth line or before the final couplet, signifying a transition in the poem's approach to its subject. This could manifest as a change in the emotional tone of the writing, or a shift in the nature of the argument or narrative being presented.