In music theory,
fake books and
lead sheets aimed towards
jazz and popular music, many tunes and songs are written in a key, and as such for all chords, a letter name and symbols are given for all triads (e.g., C, G7, Dm, etc.). In some fake books and lead sheets, all triads may be represented by upper case numerals, followed by a symbol to indicate if it is not a major chord (e.g. "m" for minor or "" for half-diminished or "7" for a seventh chord). An upper case numeral that is not followed by a symbol is understood as a major chord. The use of Roman numerals enables the
rhythm section performers to play the song in any key requested by the
bandleader or
lead singer. The
accompaniment performers translate the Roman numerals to the specific chords that would be used in a given key. In the key of E major, the diatonic chords are: • Emaj7 becomes Imaj7 (also I∆7, or simply I) • Fm7 becomes IIm7 (also II−7, IImin7, IIm, or II−) • Gm7 becomes IIIm7 (also III−7, IIImin7, IIIm, or III−) • Amaj7 becomes IVmaj7 (also IV∆7, or simply IV) • B7 becomes V7 (or simply V; often V9 or V13 in a jazz context) • Cm7 becomes VIm7 (also VI−7, VImin7, VIm, or VI−) • Dø7 becomes VIIø7 (also VIIm7b5, VII-7b5, or VIIø) In
popular music and
rock music, "borrowing" of chords from the parallel minor of a major key is commonly done. As such, in these genres, in the key of E major, chords such as D major (or VII), G major (III) and C major (VI) are commonly used. These chords are all borrowed from the key of E minor. Similarly, in minor keys, chords from the parallel major may also be "borrowed". For example, in E minor, the diatonic chord built on the fourth scale degree is IVm, or A minor. However, in practice, many songs in E minor will use IV (A major), which is borrowed from the key of E major. Borrowing from the parallel major in a minor key, however, is much less common. Using the V7 or V chord (V dominant 7, or V major) is typical of most jazz and pop music regardless of whether the key is major or minor. Though the V chord is not diatonic to a minor scale, using it in a minor key is not usually considered "borrowing," given its prevalence in these styles. == Diatonic scales ==