Music Theory of Roman Numerals: 3 Crazy Things You Must Know

The technical name of using Roman Numerals to represent chords is Roman Numeral Analysis. Roman Numeral Analysis was first used in the 17th century. It is a music theory concept that allows musicians to quickly and easily communicate about chords, chord progressions, keys, modes etc… So let’s get into the music theory of roman numerals.

Explanation: The Music Theory of Roman Numerals

Let’s begin by examining an example: say you see the roman numeral of a capital I under a chord.

Number: The Music Theory of Roman Numerals

The I, simply stands for one. It is the triad (three notes) that starts with the root or the first note in the key. So in C major, the I is the C Major Chord.

Capitalization: The Music Theory of Roman Numerals

The capital I stand for the C Major chord, and so the lower case i is the C Minor Chord!

It’s really that easy

Here are some more examples so you can get it down!

music theory of roman numerals metronome style
You’ll understand in no time!

The Major Key Chords

– The I symbolizes a major chord on the root.

– ii means you are playing a minor chord with two half steps down from tonic (root).

– iii is a minor chord with three half steps up from tonic (root).

– IV stands for a major chord with four half steps up from the root.

– V means you are playing a dominant chord five-half steps above the root.

– vi is a minor chord six half steps below the root.

– viio is a diminished chord seven half steps below the root.

Triad Inversions: The Music Theory of Roman Numerals

Roman Numerals are sometimes found with additional numbers (Arabic alphabet) next to them. These numbers indicate which inversion is being played. There are three different types of music chord inversions for a simple tonic triad.

For C Major they are:

First Inversion = C-E-G (the normal way you play the chord)

Second Inversion = E-G-C

Third Inversion = G-E-C

All that is changing is the voicing, the notes themselves actually stay the same the entire time!

sheet musics
The music theory of roman numerals at it’s core is simple, but can get more complex

What do the Numbers Next to the Inversions Mean?

It’s quite simple the top number indicates the largest interval that the chord spans, and the second number is the second largest. (Note 3 and 5 are not written because it is assumed if not otherwise specified)

7th Inversions

Just like triad inversions, Roman Numerals with additional numbers next to them indicate which inversion is being played. However, for seventh chords there are four different types of inversions!

For C Major 7 they are:

First Inversion = C-E-G-B

Second Inversion = E-G-B-C

Third Inversion = G-B-C-E

Fourth Inversion = B-C-E-G

As you can see, there are more inversions because there are four notes!

There is also a fifth type of inversion which isn’t major or minor related. It’s called the diminished chord inversion. The diminished triad has two half steps between each note, so it’s the exact same notes as C Major! So you wouldn’t need to write this out with a Roman Numeral because music theory already knows that it would be an augmented chord (the raised fifth).

What does the o mean or slashed-o mean on the inversions?

The O means that the chord is diminished, as we see in the Major Key example above.

If there is a slashed-o it means the chord is half-diminished! A half-diminished chord is a special type of seventh chord that is a min7th, on top of a diminished chord.

music theory of roman numerals m

History: The Music Theory of Roman Numerals

The history of the Roman Numeral analaysis is quite interesting too! Tons of music theorists wrote about it including; Rameau, Schenker and Schoenberg. It was first seen in  a book by music theorist Andreas Werckmeister in 1698. He used the symbols to notate figured bass, which is a way of writing out music harmonies using numbers (more on that later).

The Roman Numeral Analysis was then popularized by Jean-Philippe Rameau in his book “Traité de L’Harmonie”. Rameau also wrote music (he was a composer) and used the I, II, III, IV system in his compositions.

What is figured bass?

Figured Bass or Fauxbourdon simply means to indicate harmonies with numbers instead of notes! You would write out what key you are playing in (C Major, for example) and then write out the music theory symbols that we just saw above. The numbers indicate what intervals between notes make up your chord (for more on interval see my blog post here).

Figured Bass is no longer used as a primary means of music notation today but it was really popular in the 16th century! This is the music theory equivalent of learning to read and write music in braille instead of print.

Conclusion on Music Theory of Roman Numerals

So that’s a quick overview of music theory of Roman Numerals! As you can see, it’s not too difficult to understand and is just another way of representing chords. It can be helpful to know different ways of understanding music theory in order to better communicate with other musicians. And who knows, maybe you’ll start using Roman Numeral Analysis in your music too!

That’s all for this blog piece! You might want to give this a re-read to solidify your knowledge about music theory with Roman Numerals or leave a comment if you enjoyed the read!

Mark D.

Mark D.

Hi, I'm Mark. I've been playing instruments since I was just a little kid. I've played cello and piano for a few years, and recently picked up guitar. I've produced bad music. I also run this blog where I share interesting things I've learned. I hope you Enjoy my posts!

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