The key of a musical piece or section sets the framework by which chords are derived from a common scale and reference note. A key represents a harmonic plane where related scales and chords interact. Keys have both a tonic and a tonality.
*(ex. C major, A minor, B♭major, F# minor)
A tonic is the pitch-class that serves as a key’s point of reference. (ex. G, F#, B) A tonality indicates the particular scale starting on and referencing the tonic. (ex. major, minor)
A key’s tonality can be either major or minor.
Major keys consist of chords that are built from each scale degree of a major scale (ionian).
Chords that share the same scale family are said to be diatonic.
Diatonic chords are referred to using roman numerals as a prefix (I, II, III, IV, V, VI, & VII). Each numeral represents the distance from the key’s tonic to the root of a particular diatonic chord. The suffix of each diatonic chord is the chord quality, which will vary depending on which chord type you are considering (triads, 7th chords, etc.) (ex. Imaj7, IImin7, IIIm7, etc.)
Minor keys consist of chords that are built from each scale degree of the minor scale (also called aeolian or natural minor). However, in minor keys, the V chord triad is major instead of minor. (Because raising the 3rd of the V chord from an m3 to a M3 results in stronger voice leading between the V chord and the I chord of the key, it is used to make the strongest resolution possible to the I chord. This chord is borrowed from the harmonic minor scale family.)
In minor keys, roman numerals reflect the difference in scale degrees between parallel major and minor scale by using ♭’s before the numeral where applicable. (I, II, ♭III, IV, V, ♭VI, ♭VII)
In music notation, keys are indicated on a musical staff using key signatures, which display the order and number of sharps or flats that make up a given key.
Order of #’s:
Order of Flats:
Flats (♭’s)are also listed in the order in which they are generated moving counter-clockwise from C in the Circle of Fifths.
B♭ E♭ A♭ D♭ G♭ C♭ F♭ (“BEAD” “GCF” (mnemonic device))
There are many more harmonic planes that exist beyond major and minor using other scales. A modality is nearly identical to a key, but is derived from a scale or mode that is not major (Ionian) or minor (Aeolian). Modalities have a tonic that functions as a central focus that harmonic motion tends to resolves towards.
(ex. F Dorian, B♭Mixolydian, F# Lydian♭7)
