"Sugar Plum" is a jazz

Jazz

Jazz is a musical style that originated at the beginning of the 20th century in African American communities in the Southern United States. It was born out of a mix of African and European music traditions. From its early development until the present, jazz has incorporated music from 19th and 20th...

 song

Song

In music, a song is a composition for voice or voices, performed by singing.A song may be accompanied by musical instruments, or it may be unaccompanied, as in the case of a cappella songs...

 by American

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 jazz pianist

Pianist

A pianist is a musician who plays the piano. A professional pianist can perform solo pieces, play with an ensemble or orchestra, or accompany one or more singers, solo instrumentalists, or other performers.-Choice of genres:...

 Bill Evans

Bill Evans

William John Evans, known as Bill Evans was an American jazz pianist. His use of impressionist harmony, inventive interpretation of traditional jazz repertoire, and trademark rhythmically independent, "singing" melodic lines influenced a generation of pianists including: Chick Corea, Herbie...

 (1929–1980). It features on The Bill Evans Album

The Bill Evans Album

The Bill Evans Album is an album by jazz pianist Bill Evans, released in 1971.At the Grammy Awards of 1972, The Bill Evans Album won the Grammy Award for Best Jazz Instrumental Solo and the Best Jazz Performance by a Group awards....

 (1971). Evans reportedly wrote the song for his wife Nenette Evans. The form of the song is an extension of the typical jazz standard

Jazz standard

Jazz standards are musical compositions which are an important part of the musical repertoire of jazz musicians, in that they are widely known, performed, and recorded by jazz musicians, and widely known by listeners. There is no definitive list of jazz standards, and the list of songs deemed to be...

. The song has no melody

Melody

A melody , also tune, voice, or line, is a linear succession of musical tones which is perceived as a single entity...

, but instead is defined by a set of 8-bar chord changes that ultimately cycles through the circle of fourths; in this case, all twelve major

Major chord

In music theory, a major chord is a chord having a root, a major third, and a perfect fifth. When a chord has these three notes alone, it is called a major triad...

 keys

Key (music)

In music theory, the term key is used in many different and sometimes contradictory ways. A common use is to speak of music as being "in" a specific key, such as in the key of C major or in the key of F-sharp. Sometimes the terms "major" or "minor" are appended, as in the key of A minor or in the...

 (via ii-V-I progressions). Evans creates his own improvised melodies over each chorus. It begins in G major

G major

G major is a major scale based on G, with the pitches G, A, B, C, D, E, and F. Its key signature has one sharp, F; in treble-clef key signatures, the sharp-symbol for F is usually placed on the first line from the top, though in some Baroque music it is placed on the first space from the bottom...

, then C major

C major

C major is a musical major scale based on C, with pitches C, D, E, F, G, A, and B. Its key signature has no flats/sharps.Its relative minor is A minor, and its parallel minor is C minor....

, F major

F major

F major is a musical major scale based on F, consisting of the pitches F, G, A, B, C, D, and E. Its key signature has one flat . It is by far the oldest key signature with an accidental, predating the others by hundreds of years...

, B-flat major, E-flat major, etc. The chord progression as described by Roman numerals is as follows:

/ I / repeat / bVII / repeat / I / repeat (ii—V--) / I / (of new key)

This translates to:

/Gmaj7/ /Fmaj7/ /Gmaj7/ /Dm7/ /G7/ /Cmaj7/ = new key