What is the structure of a ternary form in music?

Ternary form in music is characterized by a three-part structure that is typically labeled as A B A. In this format, the first section (A) presents a theme or musical idea, which is then followed by a contrasting section (B) that introduces new material. Finally, the piece returns to the original theme from the first section (A). This return creates a sense of symmetry and balance, making ternary form a popular choice in many compositions, especially in classical music and various song structures.

The defining feature of the A B A structure is that it retains the first section while contrasting it with the second, which makes it distinct from other forms. For instance, in options that suggest forms like A A B or A B C, these don't accurately reflect the return characteristic of the ternary form, as A A B implies repetition without contrast. Similarly, A B C would suggest a linear progression without the return to the main theme present in true ternary form. The option A C A further complicates the structure by introducing a new section (C) without the contrasting middle section typically found in ternary form.