What is one reason certain key signatures are used?

Answer 1

One reason certain key signatures are used is to create a specific mood or tonal quality in a piece of music. Different key signatures can evoke different emotions and aesthetics, such as bright and cheerful in major keys, or dark and mysterious in minor keys. Key signatures also play a role in the overall structure and harmonic progression of a composition, as certain chords and progressions are more naturally suited to specific keys.