How Chords are Formed

In any give key certain chords are more common then others. For example in the key of C, the chords C, F and G are usually present, and quite often they are complemented with Am, Dm, and Em. The reason for this is each key has it’s own set of chords constructed from the notes of it’s scale. This is basic music theory and will work starting with any note. We will start with C, consider the scale of C major:

CDEFGABC
IIIIIIIVVVIVIIVIII

Chords are constructed by notes that are a 3rd apart in it’s scale. So the following positions would give us the root major chord of a key:

IIIIII

Using the C major scale written above, chords can be constructed by placing 2 third intervals above each note. So a C chord has C, E and G in it.

Here are the chords of the key of C and how they are constructed:

Chord
Constructed
CDmEmFGAmBo
C ScaleCDEFGAB
IIIEFGABCD
VGABCDEF

The chords are always named according to their root note. They are chords in the key of C because they only contain notes from the C scale. This method of constructing chords can be applied to form the chords of any major scale. The result will always produce the chords of whatever root note you start with.

Scale NoteIIIIIIIVVVIVII
Chord Constructedmajorminorminormajormajorminordiminished

Chord Substitutions

The chords studied so far involve the placement of 3 notes. The root note of the chord and the 2 third interval notes above it. This method of building chords can be extended by adding another note illustrated below. These chords could then be substituted for chords in the key of C, to color things up.

Chord
Constructed
Cmaj7Dm7Em7Fmaj7G7Am7Bo7*
C ScaleCDEFGAB
IIIEFGABCD
VIIBCDEFGA
VGABCDEF

From this example chords for any key can be substituted by using the chart below:

Scale NoteIIIIIIIVVVIVII
Chord Constructedmajor seventhminor seventhminor seventhmajor seventhseventhminor seventhhalf diminished seventh