This fugue in C minor is from Johann Sebastian Bach's Well Tempered Clavier, also known as the 48 Preludes and Fugues. The fugue is in 3 parts for most of the first page, becoming darker as the 4th part is added in the lowest voice. The Fugue uses all the devices associated with the form, including obvious inversions (where the tune is played upside down) and augmentations (where the tune is played at half speed). The voices pile up towards the end bringing the work to a dramatic close. Bach's Preludes and Fugues come in matched pairs in the same key, and are often (though not always) played as a pair in the order Prelude first and then Fugure. Here is the corresponding Prelude for this Fugue, also in C minor. A must for any serious student of piano, Book 1 and Book 2 are available from Sheet Music Plus.