First, a recap of some material in the All Things Major tutorial; this will help in understanding some of the discussion further down the page.
To distinguish how a chord functions (how it works in the scale it comes from); we identify it using Roman numerals.
- We use uppercase Roman numerals to indicate Major chords and chords that contain a Major 3rd above the tonic of the chord.
- We use lowercase Roman numerals to indicate minor chords and chords that contain a minor 3rd above the tonic of the chord.
- We use the chord tone number (3, 5, etc) and a # or b to indicate any alteration to any chord tone.
Using these rules, we can identify the chords built above the major scale and harmonic minor scale as follows:
Further, when we are discussing individual key centres, we usually use
- Upper case letters for major keys and
- lowercase letters for minor keys
Why we don't use stacked 3rds to describe chords
Sometimes major chords are said to be a major third plus a minor third stacked above each other.
In the same way, minor chords are said to be a minor third plus a major third stacked above each other.
The same applies to diminished chords: two minor thirds stacked above each other.
In each case, this approach ignores the fifth above the root, leading to difficulties in recognising and understanding later concepts such as altered fifths and chord extensions to the 7th, 9th and 13th.