Roman Numeral Analysis In Jazz, Pop and Rock
What are Roman Numerals?
In addition to using standard chord symbols (e.g. Cmaj7, E7, etc.) we also use Roman Numeral Analysis. Roman numerals have the benefit of helping musicians easily transpose a piece to any key. As long as you are familiar with how to play chords in every key, and the scale degrees of each key, you can quickly play a song in all 12 keys with a Roman numeral chart. This is in contrast to the standard chord symbol chart, which is only helpful for one key.
Roman numerals are built off scale degrees, the seven tones of a major scale. Another way to say this is that the Roman numeral notes are diatonic, they belong to the major scale of the given key. In the key of C, these notes are C (1), D (2), E (3), F (4), G (5), A (6), B (7).
Using the notes of the home key (in the case of C, all white notes of the C major scale) we build triads upon the scale tones. Capital case indicates a major triad, while lower case indicates a minor triad. The lower case with degree sign° means diminished. This is a triad with a flat 3 and flat 5.
It is important to realize that when someone refers to “the 2 [chord]” in the key of C, they are referring to a D minor chord in Roman Numeral Analysis.
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You’ll notice that Roman numeral symbols themselves can change depending on the key you’re in. In this case we’re in the key of A minor.
You may also be in a major key like C major, and the composer has decided to use a notes that doesn’t not correspond to the standard Roman numerals. This is normal and the Roman numeral symbols will change capitalization to reflect that change. For example, if our piece is in the key of C major, a D major chord will be written as II, instead of lowercase ii.
One can also build 7th chords on the scale tones.
As aforementioned, chords are not limited to their natural quality within the Roman Numeral system. Each chord can be modified to minor, half-diminished, fully-diminished, etc.
You can also use accidentals (sharp and flats) to deviate from the scale degrees. In the key of C, a bII (flat 2) would correspond to a Db chord instead of a D chord. Likewise, the bVI chord would correspond to the Ab rather than A.
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