Roman numerals (and the number system)

Roman numerals (and the number system)

We have seen that it is possible to build chords on the tones of the major or minor scale (the diatonic chords).

Often, these chords are not referred to by their name, but by a number. And not a regular number like 1 or 6, but with Roman numerals.

In case you forgot all about them, here are the Roman numerals 1 to 7:

1	2	3	4	5	6	7
I	II	III	IV	V	VI	VII

If we were to write the diatonic chords from the C major scale using Roman numerals, it would look like this:

C	Dm	Em	F	G7	Am	Bdim
I	ii	iii	IV	V7	vi	vii°

Notice the following:

• Major chords (C and F) are written using capitals.
• Minor chords (Dm, Em and Am) are in lower-case.
• The dominant-7 chord (G7) is written as V7.
• The diminished chord (Bdim) is written as vii°

Occasionally, you may also see the following notation:

C	Dm	Em	F	G7	Am	Bdim
I	IIm	IIIm	IV	V7	VIm	VII°

Why use these Roman numerals instead of the chord names? Because using the numbers allows us to talk about chords and chord progressions independently of the key.

For example, the chord progressions C F G7 C and F Bb C7 F can both be written as I IV V7 I.

The first is in the key of C and the second in the key of F, but otherwise they are identical:

Roman numerals:	I	ii	iii	IV	V7	vi	vii°
Key of C:	C	Dm	Em	F	G7	Am	Bdim
Key of F:	F	Gm	Am	Bb	C7	Dm	Edim

One advantage of using numbers instead of chords is that it becomes easy to transcribe a piece from one key to another.

Example. Here is the beginning of Misty in the key of C:

        C          Gm            C7          F
Look at me, I'm as helpless as a kitten up a tree

Suppose you want to play it in another key, say G. First, you replace the chord names with Roman numerals:

        I          Vm            I7          IV
Look at me, I'm as helpless as a kitten up a tree

Then you look up the chords for the new key and fill them in:

        G          Dm            G7          C
Look at me, I'm as helpless as a kitten up a tree

The principle works the same for the chords from a minor scale, although the symbols are slightly different (because the chords have different qualities).

For example, the key of A minor:

Am	Bdim	C	Dm	E7	F	G7
i	ii°	III	iv	V7	VI	VII7

It is also possible to use Roman numerals to describe chords that are not diatonic. In other words, chords that are borrowed from other keys.

For example, the chord bIII is the 3rd chord (III), in major (uppercase letters), lowered by a half-step (b). In the key of C, this would be the Eb major chord.

You may also see a sharp symbol combined with a Roman numeral: #IV in the key of C is the F# major chord.

It is not uncommon to add a qualifier to the Roman numeral. Examples: IVmaj7, II7, #IVdim7. To find the real chord, substitute the Roman numeral for the n-th chord from the scale.

You may have heard of the Nashville Number System. This is the same principle, although it works with plain-old numbers instead of Roman numerals. So instead of II-V-I you’d see 2-5-1, but they both mean the same thing.

Solfege is yet another system, except that it doesn’t use numbers, but syllables:

1	2	3	4	5	6	7
Do	Re	Mi	Fa	Sol	La	Ti

And finally, each of the diatonic chords can also be given a name that more-or-less describes its function. Different chords have different functions in their key. I’ll keep the details for a future article, so I’ll simply give you the list here:

1	Tonic
2	Supertonic
3	Mediant
4	Subdominant
5	Dominant
6	Submediant
7	Leading tone (or subtonic)

So now you know that when people talk about the “I-chord” or “tonic”, they mean the first chord from the key.