What is this secret chord number system? You’re hearing people talk about “One, Four, Five” chords progressions. And you’re seeing chords written as I, vi, ii, V, I. What the heck are they talking about?
If you’ve been hearing the “number system” helps a lot, it does. And its not too tricky.
You need to know your major scale shape
Knowing the major scale shape is a prequisite for understanding the chord number system so here’s the shape if you need a recap.
But what we’re NOT GOING TO DO is to use this scale to make solos, melodies or riffs. And we’re NOT going to be playing it up and down as part of our practice. NO! We are using the Major Scale Shape AS A TOOL to get other information.
Here’s the method: if we number the notes in the Major scale, we get notes numbered 1-7. Then, we take each one of those seven notes and use it as a starting point (or Root note) to build a group of seven chords.
The laws of harmony mean the chord type (or gender) of these chords is already set:
The One, Four and Five chords are always MAJOR
The Two, Three and Six chord are always Minor
The Seven Chord is alway Diminished.
The rules of chord gender within a single (Major) key
The prescribed gender order of the chords is:
1 chord - Major
2 chord - minor
3 chord - minor
4 chord - Major
5 chord - Major
6 chord - Minor
7 chord - diminished
Want to remember this order? Download this catchy little mp3
This group of 7 chords is called a Key. You can create chord progressions by choosing any chords in a Key, in any order and they will sound good together.
What do the Roman numbers mean?
It’s basically 1-7 but written as the Romans did.
1 = I
2 = ii
3 = iii
4 = IV (one before five)
5 = V
6 = vi (one after five)
7 = vii (two after five)
The I chord’s letter name is always the name of your Major key. So if your I chord is a G, the key is G Major.
What’s with the uppercase and lowercase letters in the chord numbering system?
Upper and lowercase letters are used in chord numbering to tell you the chord’s gender.
UPPERCASE = MAJOR
lowercase = minor
lowercase with a tiny circle (º) = diminished
Why use Roman Numeral in chords?
It’s a shorthand. Both verbally and visually.
Verbally, a dude at a jam can call “It’s a ii, V, I in G. Let’s hit it” and everyone knows the chords rather than requiring the same dude to be more lengthy “The chords are A minor, C major and G major. Let’s hit it”
Visually, your quick scribble showing I, iv, ii, V, I for the verse and vi, iii, V for the bridge can give you all the information about a song at-a-glance and not take up more than 2 lines on paper.
Practically, using the number system makes chord progressions more “portable” when they need to be transposed to other keys to fit with a singer’s vocal range.
Where do other chords like 7th chords fit?
The above prescribed rules of chord gender extend and are slightly adjusted to accomodate extended chords (chords containing 4 pitches or above)
I chord - Major 7
ii chord - minor 7
iii chord - minor 7
IV chord - Major 7
V chord - dominant 7
vi chord - minor 7
viiØ chord - half diminished 7, or (Min 7 Flat 5)
Exceptions in chord numbering
In some genres like the blues every chord is a dominant 7 chord, so you might see it written as: I7, IV7, V7.
Other times, chord progressions may borrow chords from other keys, and be written with as lowercase instead of UPPERCASE.
E.g. A common songwriting motif is playing a IV chord (MAJOR) then following it with a minor version of the same chord. This would be written IV, iv.
And those Neo Soul chords?
If you’re wondering how your cool Neo Soul chords like the Min11, Maj13 and 7#9 fit into this its simple: treat them as extensions of their root categories chords (as that’s exactly what they are).
Minor 11 chords are Minor 7s with 2 additional notes, so treat them as ii, iii or vi’s.
Maj13 are Major 7 chords with 3 notes on top, so treat them as I or IVs
7#9 chords are dominant 7th chords with one additional note, so treat them like a V chord.
Got questions on Roman Numerals in chords?
That’s what the comments box is for! Drop your questions in their.