Understanding numbers & numerals in music keys (lesson)

SixStringSage

Have you heard of a 1-4-5, or seen something like I–V–vi–IV, but wondered what it means?

You want to play music, not be a mathematician or learn Roman numerals, right?

Right!

So let’s demystify this together — the good news is it’s actually really simple and we can get through this quickly and stress-free.

As usual, it begins with the major scale. Let’s take C major, because it has no sharps or flats. The notes, in order, are:

C D E F G A B, then back to C again.

We could refer to these as letters/notes, like C or A or G.

But we can also refer to them as the number in the order they appear. We do this by starting with 1 and assigning a number to each letter, in consecutive order, like this:

C = 1

D = 2

E = 3

F = 4

G = 5

A = 6

8 = 7

C = 8, or 1, the same note but an octave higher

So when someone says “let’s play a 1 4 5 progression in the key of C” what they mean is you’ll be playing the chords C, F, and G.

You might now be wondering if it’s really that simple. And the answer is yes, it is. It can look very confusing to begin with but it’s very simple.

But how do you know if they should be major or minor chords?

The numbers help us here too. The notes in a key will differ — for example, a C major scale and E major scale have different notes. But the numbers are always consistently major or minor.

The system is as follows:

The 1, 4, and 5 notes are played as major (the 5 is technically a “dominant” chord meaning it also has a flat 7, but it can played as a regular major too).

The 2, 3, and 6 notes are played as minor.

The 7 is played as a “diminished” chord, which means the 5 is flattened as well. But as it’s got a flat 3, we can refer to it as a type of minor chord in this explanation.

So in any major key you choose, you use the above system to know which chords would be played as major or minor (or dominant and diminished).

Understanding Roman numerals

Roman numerals tell us similar information, except they explicitly tell us how to play a chord. This is how a major key is written with numerals:

C = I

D = ii

E = iii

F = IV

G = V7

A = vi

B = vii°

You’ll notice that some of these are upper case and others are lower case, and this is a clear instruction to us:

Uppercase numerals are played as **major chords**

Lowercase numerals are played as **minor chords**

The 7 in the G means dominant and that symbol in the B numeral means it’s diminished.

So, when someone says “Let’s play a 1 4 5 progression in the key of C” they mean you’re going to play C major, F major, and G major or G dominant.

This works for any key, too. Let’s take F major:

F = 1 = I

G = 2 = ii

A = 3 = iii

B♭ = 4 = IV

C = 5 = V

D = 6 = vi

E = 7 = vii°

So a 1 4 5 here would be F major, Bb major, C major or C dominant.

A sample progression

At the start of this post I mentioned this progression: I–V–vi–IV. This is common in multiple genres, and hopefully you can now understand what it means:

I

V

vi

IV

That’s 1, 5, 6, 4. Uppercase numerals are major, lowercase are minor, so the 1, 5, and 4 are played as major and the 6 is played as minor (the 5 can be dominant if you prefer).

In the key of C major, this progression would be C major, G major, A minor, F major.

These numerals are consistent across all the major keys — the 1 (I) is always major, the 2 (ii) and 3 (iii) are always minor, the 4 (IV) is always major, the 5 (V) is dominant or major, the 6 (vi) is minor, and the 7 (vii°) is diminished.

When you know this, you can always work out the exact chords in any major key, even if you haven’t memorised them yet.

Of course, this doesn’t mean you can’t ever play different chords there. It’s not uncommon to play a major 4, then switch to a minor 4, then resolve to the 1, for example. But when you’re around people who talk in the number system, or you’re learning something that uses numbers and numerals, this is all it is.

And an added bonus is this system is used by musicians in general, unlike tab which is more guitar-centric. So by learning this, you’ll be able to confidently communicate with other musicians.

This was first published in my guitar newsletter