Understanding Diatonic Chords
It's handy to understand how certain chords fit naturally into a particular key. Using each scale degree in a particular key as a base, each note can be built into a chord.
As with single notes, every key has certain chords which fall naturally into that key. Whether or not they do so is determined by the notes in that chord. If the chord contains no chromatic notes (notes not naturally occurring in that key), it is regarded as a diatonic chord (a chord which occurs naturally because it contains notes only from the diatonic scale). Otherwise, it is a chromatic chord (that is, a chord containing chromatic notes).
For instance, the chord F major occurs naturally in the key of C major because each note in that chord (F, A and C) also belongs in the key of C major. However, D major is a chromatic chord when played in the key of C major because it contains an F# which does not belong in that key.
First, we'll look at the chords in the key of C major, using each of its notes as a chord root (the note from which the chord takes its name). The chords that we'll build will all be triads (chords with three notes), although more complex chords could also be formed.
The chords are all formed by adding notes to the root note in thirds. A third means the next note but one in the scale. For instance, beginning with C, we skip D and add E, then skip F and add G. Thus our first chord, C major, contains the notes C, E and G. Set out in the table is the C major scale, along with the other notes in each respective triad.
Notice that each note in each triad belongs in the key of C major. There are no sharps or flats. If, for instance, we had a C# in the number VI chord, we would have the chord A major. But the C# does not belong in this key, therefore the A major chord does not naturally belong there either; in the key of C, it is a chromatic chord.
There is also a pattern in the above table, as follows:
This pattern holds true for every major key. It is important that you realise that this does not mean that these are the only chords that can be used in these keys. This is by no means true. These are only the chords which naturally belong in that key, and are therefore to be expected.
In point of fact, you can put any chord in any key, provided the result is pleasing to the ear. Please note that in setting out this chart, I have not worried about including enharmonic (C# and D♭ are called enharmonic equivalents since they are exactly the same note.) keys such as C# or F#.
For more information as well as a complete chart on diatonic chords in major keys, buy Contemporary Music Theory. (This link will take you to Createspace.com, a subsidiary of Amazon.)Understanding Scales | Understanding Chord Structure | Understanding Diatonic Chords | Understanding Minor Scales | Diatonic Chords in Minor Keys | Scale Degree Names | Chord Substitution - Extended Chords | Chord Substitution - Overlapping Chords | Improvisation - Arpeggios | Improvisation - Major Scales | Improvisation - Pentatonic Scales | Improvisation - Blues Scales