What is the primary function of the left pedal on a piano?

The primary function of the left pedal on a piano, known as the una corda pedal, is to dampen the strings. When this pedal is pressed, it shifts the action of the hammers in a grand piano so that they strike fewer strings. For example, in a standard concert grand piano, pressing the left pedal allows the hammer to hit only one string (or two strings, depending on the note) instead of all three, producing a softer and more muted sound. This use of the left pedal is particularly useful for creating delicate passages in music where a softer timbre is desired.

Other options may pertain to different aspects of piano playing, but they do not correctly describe the function of the left pedal. The right pedal, for instance, increases sustain by allowing the dampers to lift off the strings, enabling notes to resonate longer, while the middle pedal (in some pianos) is used for a specific sustain effect without affecting all the strings. In contrast, softening the sound as defined by the other options relates to the dynamic control of volume rather than the specific mechanical design and function of the left pedal.