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As with other musical elements, the early 20th century was a time when structure and form were developed in many different ways. A number of forms evolved in popular and world music traditions.

Popular music

12-bar blues

This form was popular in rock ’n’ roll, and was originally the basis of blues music.

Verse-chorus structure

The structure of verse-chorus became the foundation for 20th century popular music. A chorus was the section that was repeated and had the same music and words. Verses had the same music but different lyrics. Within this structure, songwriters also included intros and outros, the middle 8, instrumental breaks and bridges between verses and choruses.

32-bar structure

What is known as the 32-bar structure became popular in early 20th century US popular music, and can be found in many of George Gershwin’s and Cole Porter’s songs. The form is AABA, each section being eight bars long. A famous example is Over the Rainbow by Harold Arlen.

World music

Below are examples of two World music styles that demonstrate how different music from different parts of the world are from Western Classical music.

Indian raga

Indian ragas are based on the rag - an Indian scale - and are quite different from Western styles. A typical raga has the following structure:

• Alap - slow and unmetred. An unaccompanied sitar explores and improvises on the notes of the raga.
• Gat 1 - a fixed composition that is heavily ornamented.
• Gat 2 - the tempo becomes faster with more improvisation.

You can hear an example of raga in Rag Desh:

Samba

Samba is one of many world music styles that is based on ostinatos. Each instrument in the band has its own ostinato within each section. There can be as many as six ostinatos per piece. Each of the sections is called a groove. Between these grooves are breaks and mid-sections.