What is the main purpose of the circle of fifths?

The circle of fifths serves primarily to illustrate the relationships between keys with sharps and flats. It provides a visual and conceptual framework that helps musicians understand how different keys are related to each other.

When moving clockwise around the circle, each step represents a fifth interval, leading to keys that have one more sharp than the previous key. Conversely, moving counterclockwise introduces keys with one more flat. This organization allows musicians to easily identify relative major and minor keys, making it simpler to compose, arrange, or transpose music. It establishes a clear connection between different keys, enhancing a musician's ability to navigate through various harmonic structures effortlessly.

While the other options touch on different aspects of music theory, they do not accurately capture the primary function of the circle of fifths. For instance, the dynamic range of chords relates more to expressiveness and volume rather than key relationships. The outline of a composition's structure is more concerned with form and development rather than key interactions. Similarly, tempo and rhythm are components of musical performance rather than key relationships. Thus, the circle of fifths remains an essential tool for understanding key signatures and their interrelations in Western music.