Augmentation

What it means

Augmentation is the lengthening of a theme's or motif's note values, usually to double their original duration: eighth notes become quarter notes, quarter notes become half notes. The pitch sequence and its intervals stay the same; only the pace at which it unfolds sounds slowed down.

In the notation

In the score, augmentation shows up simply as the lengthened note values themselves; there is no separate sign for it. In earlier centuries' polyphony, an instruction for a voice to be played in augmented values was sometimes written as a canon inscription such as per augmentationem above the part, rather than being written out in full.

Musical use

Augmentation is one of the classic techniques of thematic transformation, alongside inversion and diminution. In a fugue it often appears near the close, when the subject returns in lengthened values – frequently in the bass – gaining extra weight from the broadened pace; Johann Sebastian Bach famously combined augmentation systematically with the original form, inversion, and diminution of a single fugue subject in his late cyclical work on the art of fugal writing. In a canon, one voice can restate the theme in augmentation while another carries it in its original values.

Augmentation should be distinguished from stretto, where thematic entries are compressed in time rather than lengthened in note value; both techniques can occur together within the same fugue. Its direct opposite is diminution, the shortening of note values.

Performance practice

When you play or conduct a fugue with an augmented subject entry, it helps to sing the theme in its original form first, so you immediately recognize its return in the stretched-out version and can bring it out accordingly in performance.