The Observed Phenomena of Chords in Popular Music
Chord sequences are a staple in modern popular music.
It is possible to have a song without well-defined chord sequences, but that is very much the exception.
Rules About Chords
The most common chords are three-note chords where all the notes are harmonically related, ie a major chord or a minor chord, and all the notes of the chord are also notes of the scale. (On a 'white-note' scale, this is one of six chords: C, G, F, Dm, Am and Em.)
But chords can, and often do, vary from this 'standard':
- There can be more than three notes
- There can be less than three notes
- There can be non-scale notes (but if there are, most likely only one note will be non-scale, and it most likely won't be the bass note of the chord).
Chords are an important part of most songs, but a chord sequence by itself doesn't make music. Any kind of chord sequence only sounds musical because you are paying attention to one note at a time from each chord, which means that you are listening to a melody.
Rules About Chord Sequences
There are no absolute rules for what chords make up a sequence, but there are various kinds of things that often happen:
- Consecutive chords share two notes with each other.
- Alternatively, consecutive chords don't share notes with each other.
- Notes within chords in the sequence form a chromatic sequence.
- Note within chords in the sequence form a sequence travelling up or down the scale.
- Chords in the sequence form a sequence of fifths.
- Sometimes the chords initially follow a certain type of sequence, but then the trajectory changes (perhaps because the sequence cannot continue without 'leaving' the scale).
- The chord sequences starts on the 'home chord', which is the home chord of the scale, and ends on the 'home chord'.
- Or, the chord sequence starts on the 'home chord', and endlessly cycles, so the return to the 'home chord' is always the start of the next cycle.
Chords make a melody sound better, but, a melody sounds melodious even if unaccompanied by any chords.
Stronger notes in the melody usually match the chord, so the chords are implicit in the melody itself.
The chords usually change on the strongest part of the beat, ie at the beginning of a bar, and the next best choice of place to change would be half-way through the bar.
Chords, and 'Steady State' in Cortical Maps
According to my hypothesis of Constant Patterns of Activity and Inactivity, musicality results from patterns of activity and inactivity in cortical maps which remain constant over a certain time period.
Chords partly fit this model. The "current chord" would seem to constitute an element of steady state in some cortical map which is responsible for perceiving the current harmonic state of the music.
But then the chord changes, so at the moment of change there is not a steady state.
Maybe, it's sufficient that the 'chordal state' in the listener's brain is constant most of the time, and that when change occurs it occurs very quickly, so the loss of musicality due to this change is minimized. Also, perhaps it is important that other aspects of the listener's brain activity state are not changed at the moment of chord change, so that overall there is a persistent high-level of constancy in cortical activity patterns.