The structure of a typical Italian sonnet of the time included two parts that together formed a compact form of "argument". First, the octave forms the "proposition", which describes a "problem" or "question", followed by a sestet (two tercets) which proposes a "resolution". Typically, the ninth line initiates what is called the "turn", or "volta", which signals the move from proposition to resolution. Even in sonnets that don't strictly follow the problem/resolution structure, the ninth line still often marks a "turn" by signaling a change in the tone, mood, or stance of the poem.