Monotonality is a theoretical

Music theory

Music theory is the study of how music works. It examines the language and notation of music. It seeks to identify patterns and structures in composers' techniques across or within genres, styles, or historical periods...

 concept, principally deriving from the theoretical writings of Arnold Schoenberg

Arnold Schoenberg

Arnold Schoenberg was an Austrian composer, associated with the expressionist movement in German poetry and art, and leader of the Second Viennese School...

 and Heinrich Schenker

Heinrich Schenker

Heinrich Schenker was a music theorist, best known for his approach to musical analysis, now usually called Schenkerian analysis....

, that in any piece of tonal music only one tonic

Tonic (music)

In music, the tonic is the first scale degree of the diatonic scale and the tonal center or final resolution tone. The triad formed on the tonic note, the tonic chord, is thus the most significant chord...

 is ever present, modulations

Modulation (music)

In music, modulation is most commonly the act or process of changing from one key to another. This may or may not be accompanied by a change in key signature. Modulations articulate or create the structure or form of many pieces, as well as add interest...

 being only regions or prolongation

Prolongation

In music theory, prolongation refers to the process in tonal music through which a pitch, interval, or consonant triad is able to govern spans of music when not physically sounding...

s within, or extensions of the basic tonality

Tonality

Tonality is a system of music in which specific hierarchical pitch relationships are based on a key "center", or tonic. The term tonalité originated with Alexandre-Étienne Choron and was borrowed by François-Joseph Fétis in 1840...

.

History

Schoenberg laid out his concept of monotonality in his book Structural Functions of Harmony, writing that: "According to this principle, every digression from the tonic is considered to be still within the tonality, whether directly or indirectly, closely or remotely related. In other words, there is only one tonality in a piece, and every segment formerly considered as another tonality is only a region, a harmonic contrast within that tonality...subordinate to the central power of [its] tonic. Thus comprehension of the harmonic unity within a piece is achieved."