In music, Roman numeral analysis uses Roman numerals to represent chords. The Roman numerals (I, II, III, IV, ...) denote scale degrees (first, second, third, fourth, ...); used to represent a chord, they denote the root note on which the chord is built. For instance, III denotes the third degree of a scale or the chord built on it. Generally, uppercase Roman numerals (such as I, IV, V) represent major chords while lowercase Roman numerals (such as i, iv, v) represent minor chords (see Major and Minor below for alternative notations); elsewhere, upper-case Roman numerals are used for all chords. In Western classical music in the 2000s, Roman numeral analysis is used by music students and music theorists to analyze the harmony of a song or piece.
In the most common day-to-day use in pop, rock, traditional music, and jazz and blues, Roman numerals notate the progression of chords in a song. For instance, the standard twelve bar blues progression is I (first), IV (fourth), V (fifth), sometimes written I7, IV7, V7, since the blues progression is often based on dominant seventh chords. In the key of C (where the notes of the scale are C, D, E, F, G, A, B), the first scale degree (Tonic) is C, the fourth (Subdominant) is F, and the fifth (Dominant) is a G. So the I7, IV7, and V7 chords are C7, F7, and G7. In the same progression in the key of A (A, B, C♯, D, E, F♯, G♯), the I7, IV7, and V7 chords would be A7, D7, and E7. Roman numerals thus abstract chord progressions, making them independent of the key, so can easily be transposed.
Roman numeral analysis Wikipedia
Roman numeral analysis is the use of Roman numeral symbols in the musical analysis of chords. In music theory related to or derived from the common practice period, Roman numerals are frequently used to designate scale degrees as well as the chords built on them. In some contexts, arabic numerals with carets are used to designate scale degrees (); theory related to or derived from jazz or modern popular music may use Roman numerals or arabic numbers (1, 2, 3, etc...) to represent scale degrees (See also diatonic function). In some contexts an arabic number, or careted number, may refer also to a chord built upon that scale degree. For example, or 1 may both refer to the chord upon the first scale step.
Gottfried Weber's Versuch einer geordneten Theorie der Tonsetzkunst (Theory of Musical Composition) (Mainz, B. Schott, 1817–21) is credited with popularizing the analytical method by which a chord is identified by the Roman numeral of the scale-degree number of its root. However, the practice originated in the works of Abbé Georg Joseph Vogler, whose theoretical works as early as 1776 employed Roman numeral analysis.
The current system used today to study and analyze tonal music comes about initially from the work and writings of Rameau’s fundamental bass. The dissemination of Rameau’s concepts could only have come about during the significant waning of the study of harmony for the purpose of the basso continuo and its implied improvisational properties in the later 18th century. The use of Roman numerals in describing fundamentals as “scale degrees in relation to a tonic” was brought about, according to one historian, by John Trydell’s Two Essays on the Theory and Practice of Music, published in Dublin in 1766. However, another source says that Trydell used Arabic numerals for this purpose, and Roman numerals were only later substituted by Georg Joseph Vogler. Alternatives include the functional hybrid Nashville number system and macro analysis.
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 "ø" 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:E7 becomes I7 (or simply I)
F♯m7 becomes ii7 (or simply ii)
G♯m7 becomes iii7 (or simply iii)
A7 becomes IV7 (or simply IV)
B7 becomes V7 (or simply V)
C♯m7 becomes vi7 (or simply vi)
D♯ø7 becomes viiø7 (or simply vii)
In popular music and rock music, "borrowing" of chords from the tonic minor of a key into the tonic major and vice versa 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. As well, in minor keys, chords from the tonic major may also be "borrowed". For example, in E minor, the diatonic chords for the iv and v chord would be A minor and B minor; in practice, many songs in E minor will use IV and V chords (A major and B major), which are "borrowed" from the key of E major.
In traditional notation, the triads of the seven modes are the following: