Let’s take a look to see how chord progressions are put together and how they are notated.
Chords and Scale tones:
A chord can be formed from any note of the underlying scale, with that note of the scale as the root.
Where in the scale the chord falls determines the type of chord that is formed: major, minor or dim
When playing a song in major key:
- major chords are formed form the 1st (tonic), 4th and 5th scale tones.
- minor chords are formed from 2nd, 3rd and 6th scale tones
- dim chord is formed from the 7th scale tone
Roman Numeral Notation
To better understand these relationships, chords are sometimes notated using Roman numerals.
Each scale tone has its corresponding Roman numeral.
–the tonic of the scale is I
–the 2nd tone is II
etc.
Upper case signifies major chords.
Lower case for minor chords
I ii iii IV V vi vii
This type of Roman numeral notation is good in that it lets you refer to a chord type independent of any specific key.
If you hae an extended chord, the extension is added to the right of the Roman numeral.
Dom 7 chord based on the 5th of the scale is notated as V7.
m7 based on the 3rd of the scale is notated: iii7
All of these numbers are necessary to help us talk about chords in relation to one another, so that we can talk about a universal chord progression independent of a given key.
When we talk about a I IV V7 progression, you can translate that progression into whatever key you are working with: C F G7 in key of C
Bb Eb 7 in key of Bb
Composers can create chords that fall outside the underlying scale.
Just cuz the chod based ont he 3rd of the scale is naturally a minor chord doesn’t mean that you can’t put a major chord there instead.
That would make it a III chord instead of the expected iii chord.
A diatonic chord is one that falls naturally, within the underlying scale; diatonic notes are notes contained within the underlying scale or key. NOn-diatonic chords are those that contain notes that are not part of the underlying scale.
Nashville Number system
In country music, esp among studio musicians, a different type of chord sheet is often used.
This method of writing chords is called Nashville Number system, and it uses regular number instead of Roman numerals.
In Nashville Number System — everything revolves around the tonic of a given key.
Tonic chord is assigned the number 1.
Chord based on the ii of the key — a minor chord – is assigned the number 2m
Chord based on the iii of the key — minor chord, assigned the number 3m.
Major chords are distinguished by number only while minor chords have an added ‘m’.
Extensions are added as superscripts to the right of the number, sothat a dom 7 chord based on the 5th of the sale is notated as 5 (7) upper 7