Audio: chord notation (0:08)
|Natural minor (aeolian)
chord notation plays three part harmony on a piano in the key of C major followed by the key of A harmonic minor. The chord notation figure shows the score. It illustrates two ways to notate a chord: with a name written above the staff or with a number written below the staff. The chord notation table lists chords in major and minor keys:
Chord notation is based on tertian harmony and assumes that a chord has a minimum of three notes.
A chord is notated with a name or a number.
A chord name consists of the name of the root note followed by the type, or quality, of the chord. There are four types of chord that can be constructed from major thirds (M3) and minor thirds (m3):
A chord is numbered using a Roman numeral denoting the degree of the scale which forms the root of the chord:
You can notate a chord at any time. You can do it before writing, if you have a clear idea of what you want, during the writing process, to give you a clearer idea about what you are doing, or leave it until you have finished.
Chord notation is extremely useful in providing information to yourself and others about harmony. It is a flexible system but it is not comprehensive. It does not easily convey useful information about certain chords:
Now is as good a time as any to look at another subject in harmony, that of tonality and the relationship between chord, key and scale.
The notes in a scale are used to construct a chord and the key determines how the chord is notated. There is thus a direct link from a key to a chord. Is there a link the other way, can a chord define a key? The answer is no, not quite.
Take the seven note chord, ABCDEFG, as an example. Then answer the question, what is the key? Well the notes look remarkably like a major scale or one of its related modes. But which note is the tonic? It could be any of them. A chord has to be heard in context, in a chord progression with other chords, to precisely determine its key. A key is defined in harmony by a succession of chords in exactly the same way as a key in melody is defined by a succession of notes. The common methods for providing a clue to the key of a harmony are to start and end a piece of music on the tonic chord, the chord whose root is the tonic note of the chosen scale, and to return to this tonic chord at regular intervals throughout the piece to emphasise the key. The only unambiguous way to signal the key, however, is to write it in the score. Ultimately, key is defined by you, the writer, not by the notes or chords themselves.
An interesting follow on is whether there is any chord that implies a key. The surprising answer is that there is an interval which is strongly indicative of key, and it is the tritone. Seven notes that lie between a tritone in the circle of fifths constitute a scale. The presence of a tritone in a chord is highly suggestive of one of two scales. For example, the tritone BF is part of two scales, A-B-C-D-E-F-G and F#-G#-A#-B-C#-D#-E#-F-G#. These are respectively the keys of C major and F# major. A third note is required to completely identify the scale. Any third note will do. For example, the chord BDF, a B diminished chord, identifies the scale as A-B-C-D-E-F-G and implies the key of C or one of its related modes. A three note chord containing a tritone is the smallest chord which unambiguously defines a scale and is highly suggestive of key.