Ok, ok, sure. Roman Numerals are letters…. But you know what we mean. 😂

If you need it, here’s a quick refresher on reading roman numerals we only ever go to seven here, so it won’t take you long to get the system.

In the last lesson we built the diatonic chords and noticed the same pattern in every key: Major, minor, minor, Major, Major, minor, diminished. The letter names change from key to key, but the pattern never does.

Roman numerals let you talk about that pattern directly. Instead of saying "the G chord in the key of C," you say "the V chord." Instead of "the A minor chord in the key of C," you say "the vi chord." The number tells you which scale degree the chord is built on, and the case tells you the quality.

Uppercase = major. Lowercase = minor. A little circle (°) = diminished.

Numeral	Quality	In C major	In G major	In D major
I	Major	C	G	D
ii	Minor	Dm	Am	Em
iii	Minor	Em	Bm	F#m
IV	Major	F	C	G
V	Major	G	D	A
vi	Minor	Am	Em	Bm
vii°	Diminished	Bdim	F#dim	C#dim

The roman numeral is the same in every column. The letter name changes, the function doesn't. That's the whole point.

Here's an example. These three progressions sound basically the same:

• C — F — G — C (in the key of C)
• G — C — D — G (in the key of G)
• E — A — B — E (in the key of E)

They're all I — IV — V — I. The exact same pattern transposed to different keys. If you think in letter names, those look like three different things. If you think in numbers, they're obviously the same thing.

This is how working musicians think. When someone says "it's a I-IV-V," everyone in the room knows the shape of the progression regardless of what key they're about to play it in. When you analyze a song and say "the chorus is I-V-vi-IV," that analysis works in every key. You've described the structure, not just the notes.

If you're used to reading lead sheets with chord symbols, you know the pain of transposing. Someone says "let's do it in Eb instead of C" and now you're mentally converting every chord on the page.

Once you think in numbers, transposition is just... done. A I-V-vi-IV is a I-V-vi-IV in any key. You learn the progression once, and then you just need to know which letter names go with which numbers in the new key, and that’s something you are well on your way to having memorized. You don’t have to convert every chord individually.

If you play guitar with a capo, this is especially useful. Say a song is in the key of B and you want to play it with a capo on the 4th fret. You're now "in G" from your fingers' perspective, but the song is still in B. If you know the progression is I-V-vi-IV, you just play those shapes in G: G-D-Em-C. You know the numbers, you know the key your capo puts you in, and you're done.

A few conventions worth knowing:

• I is always the "home" chord. The tonic. The key itself.
• Uppercase (I, IV, V) means major quality.
• Lowercase (ii, iii, vi) means minor quality.
• ° symbol (vii°) means diminished.
• When you see V7, that means a dominant seventh chord built on the 5th degree. Extensions and alterations get added the same way they do with regular chord symbols.

You might also see Arabic numbers used the same way. "1-4-5" means the same thing as "I-IV-V." That's the Nashville Number System, which we'll touch on later in the course. Roman numerals are the standard for analysis and come up more often in theory discussions and resources.

• musictheory.net — Roman Numeral Analysis — quick interactive intro.
• Open Music Theory — Roman Numerals — more in-depth, with examples and explanations of how numerals are used in analysis.
• Roman Numeral Chord Notation — Music Theory — video walkthrough of the notation system.

• Take a song you know and figure out the key. Then identify each chord as a roman numeral. If the song is in D major and it goes D-Bm-G-A, that's I-vi-IV-V. Try this with a few songs and you'll start seeing the same numerals come up over and over.

• Head over to our (Progression Analysis Trainer)[/shed/progression-analysis/] and give it a go!