The Number System

I ii iii IV V vi vii° explained

20 min

Roman Numeral Analysis

The number system assigns a Roman numeral to each chord in a key based on its position in the scale. This lets you describe chord progressions independently of any specific key:

In C major: C=I, Dm=ii, Em=iii, F=IV, G=V, Am=vi, B°=vii°

Uppercase numerals = major chords (I, IV, V)
Lowercase = minor chords (ii, iii, vi)
° symbol = diminished (vii°)

The power of this system: the progression I-V-vi-IV means the same thing in every key. In C it's C-G-Am-F. In G it's G-D-Em-C. In D it's D-A-Bm-G. Same musical function, different notes.

The Most Common Progressions

With the number system, patterns emerge across all of music:

I - V - vi - IV: The "Axis of Awesome" progression. Used in Let It Be, No Woman No Cry, With or Without You, and hundreds more.

I - IV - V: The simplest rock/blues progression.

vi - IV - I - V: Starting on the minor chord gives a different feel. Used in many emotional pop songs.

I - vi - IV - V: The 1950s "doo-wop" progression.

ii - V - I: The backbone of jazz harmony.

These patterns work in any key because the relationships between the chords stay the same.

Nashville Number System

Working musicians (especially in Nashville) use plain numbers instead of Roman numerals: 1-4-5 instead of I-IV-V. If someone says "it's a 1-5-6-4 in G," you immediately know: G-D-Em-C.

This makes transposing instant. Want to play the same song in A instead of G? A=1, so: A-E-F#m-D. The numbers don't change, only the letter names.

This is why learning the number system is so valuable — it makes you think in terms of function rather than specific notes.

Tab Examples

e|--3--3--3--3--|--2--2--2--2--|--0--0--0--0--|--0--0--0--0--|
B|--0--0--0--0--|--3--3--3--3--|--0--0--0--0--|--1--1--1--1--|
G|--0--0--0--0--|--2--2--2--2--|--0--0--0--0--|--0--0--0--0--|
D|--0--0--0--0--|--0--0--0--0--|--2--2--2--2--|--2--2--2--2--|
A|--2--2--2--2--|-------------|--2--2--2--2--|--3--3--3--3--|
E|--3--3--3--3--|-------------|--0--0--0--0--|--------------|

G(I) - D(V) - Em(vi) - C(IV). The most used progression in pop music.

e|--0--0--0--0--|--3--3--3--3--|--0--0--0--0--|--1--1--1--1--|
B|--1--1--1--1--|--0--0--0--0--|--1--1--1--1--|--1--1--1--1--|
G|--0--0--0--0--|--0--0--0--0--|--2--2--2--2--|--2--2--2--2--|
D|--2--2--2--2--|--0--0--0--0--|--2--2--2--2--|--3--3--3--3--|
A|--3--3--3--3--|--2--2--2--2--|--0--0--0--0--|--3--3--3--3--|
E|-------------|--3--3--3--3--|-------------|--1--1--1--1--|

C(I) - G(V) - Am(vi) - F(IV). Same numbers, different key. Same feel.

Tips

I-V-vi-IV is the most common progression in popular music — recognise it everywhere

Uppercase = major, lowercase = minor — the capitalisation matters

Practice transposing: if you know a song as I-V-vi-IV in G, try it in C and D

The Nashville system uses plain numbers (1-5-6-4) — same concept, simpler notation

Practice Exercises

Write out the diatonic chords (I through vii°) for the keys of G, C, D, and A

Play I-V-vi-IV in three different keys — hear how the feel stays the same

Listen to 5 songs and try to identify the chord progression using numbers

Transpose a song you know from its original key to a new key using the number system

Try ii-V-I in C major (Dm-G-C) — this is the foundation of jazz

The Number System

Roman Numeral Analysis

The Most Common Progressions

Nashville Number System

Tab Examples

I - V - vi - IV in G major

Same progression in C major: I - V - vi - IV

Tips

Practice Exercises

Roman Numeral Analysis

The Most Common Progressions

Nashville Number System

Tab Examples

I - V - vi - IV in G major

Same progression in C major: I - V - vi - IV

Tips

Practice Exercises

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