'In Three Parts'
The basic structure for ternary form is: ABA
Often each section repeats so it becomes: AABBAA
- Section A ends in the main key, usually with a perfect cadence so it sounds like a complete piece itself.
- Section B modulates to a related key, i.e. the dominant or relative minor, before returning to the main key at the end.
- When the music returns to the A section it can vary slightly from the original A section, i.e. with ornatmentation.
- If it varies it could be called A1, but it shouldn't be so…