Short answers, pulled from the story.
Musical form describes the arrangement of rhythm, melody, and harmony that creates repetition or variation within a piece. It involves four structural elements interacting to create the larger shape of any composition: sound, harmony, melody, and rhythm.
Percy Goetschius published Lessons in Music Form in 1904 to help students understand how music is organized. This publication provided foundational concepts for understanding musical structure.
Binary form describes a piece with two sections about equal in length while ternary form presents three parts where the third repeats or contains the principal idea of the first. Greensleeves demonstrates this binary structure where the first system almost matches the second.
Sonata-allegro form serves as the most important principle of musical form from the classical period into the twentieth century. It typically casts a greater ternary form having exposition, development, and recapitulation subdivisions.
AABA song forms appear predominantly within American popular music traditions today alongside verse-chorus forms that dominate modern genres. The twelve bar blues follows an AAB pattern common across many styles.