Roman numeral chord notation is an effective way of representing the relationships among basic chords in any key. Each number represents a triad that can be built using scale degrees from that key.
Major chords are identified with uppercase Roman numerals and minor ones with lowercase letters. Their symbols also indicate whether it is minor, diminished or augmented.
I
Names of chords can be determined either by their scale degrees of construction or their function within a chord progression. Roman numerals are frequently employed in music notation to identify both its function and key. This method makes transitioning chord progressions from one key to another easy as each numeral can easily be matched up with its respective function in the new key.
Roman numerals are widely used when notating major and minor triads as well as seventh chords built upon either a major or minor scale, such as V7 chords in C major (for instance). Diminished triads may also use Roman numerals with an additional small “o” added for diminished chords – although bass voice must always correspond with inversion of Roman numeral figures; upper notes may be ordered however desired.
For seventh chords, their quality can be indicated by capitalization of Roman numerals: uppercase Roman numerals denote major triads while lowercase ones show minor or diminished ones. Half-diminished seventh chords can be identified by adding an “o” after their Roman numeral (such as (viio); full diminished seventh chords require notating them with an extra letter as in (viio7).
Roman numerals can also be an effective way to record changes to chords. For instance, a vii chord may contain altered notes, such as flat or sharp notes; therefore, to represent this change the triad will be notated as (viio).
An augmented chord is indicated with a Roman numeral followed by a plus sign (V+). This symbol can also be used for dominant seventh chords to indicate their augmentibility.
Some music theorists prefer using only uppercase Roman numerals, believing that chord qualities can be perceived intuitively. Others, including this textbook, prize distinguishing between uppercase and lowercase Roman numerals.
Roman numerals provide an easy way to identify chord types: major triads are indicated with uppercase Roman numerals while minor ones use lowercase Roman numerals. But some chords require more complex numbering systems: major triads use an uppercase Roman numeral while minor triads have a lowercase Roman numeral designation. As an example, triads with minor thirds must be written as (iv), rather than (vii), due to the incompatibility between minor chords and major scale tones; consequently they may sometimes be known as the augmented triad. As this type of triad should only ever be played in minor keys, and should never serve as a replacement for V or IV chords in minor keys, using it inappropriately can cause serious chromatic errors. For this reason, it is crucial to learn their correct numbering, even though these triads don’t usually feature prominently within major scales.