How does diminution change a fugue subject?

In the context of a fugue, diminution is a technique used to manipulate the subject by shortening the rhythmic values of its notes. Specifically, a composer may cut the duration of each note in the subject in half, or into even smaller fractions, effectively accelerating the subject's presentation.1

This technique serves as a contrast to augmentation, where the rhythmic values of the subject are doubled. Both methods are common ways for composers to vary and develop the subject throughout the course of a musical work.1