When studying jazz guitar, you quickly learn that analyzing chord progressions and transposing chords are two essential skills you need to have down. But, while you know that analyzing and transposing is important, you might not know the quickest and easiest way to accomplish these goals. This is where Roman numerals come into play.
Roman numerals are used in music to analyze diatonic and non-diatonic chords as well as make transposing any chord or progression much easier on the guitar.
In this lesson you learn what Roman numerals are, how they’re used in jazz analysis, and how to transpose chords with these numbers.
Diatonic Chords With Roman Numerals
To begin your study of Roman numerals and their use in analysis and transposition, we’ll look at diatonic chords with Roman numerals.
Here are the notes in the key of C major, written on a single string, with the number of each note below the staff.
Arabic numbers are used to identify single-notes in jazz, like scale and arpeggio notes, while Roman numerals identify chords and progression.
This makes it easier to understand a written analysis of any line or progression, as you won’t be confused if you see 1 vs. I in an analysis.
Now you add chords on top of each of those C major scale notes to form the chords in the key of C major.
Here are those chords with the Roman numerals written underneath each chord to see how they line up in the key.
Notice that the Roman numerals are the same as the Arabic numbers, 1 is I, 2 is ii, etc., as each scale note gets a chord in the key.
Once you know the notes in a key, and their related chords, you can use that to analyze chord progressions.
Here’s an example of a common jazz chord progression with Roman numerals below each chord, from the key of C major.
Minor chords are written in lowercase roman numerals, while major and dominant chords are written in uppercase roman numerals.
Now that you know how to use Roman numerals to identify chords in a key, open your Real Book and analyze diatonic chords in any song you flip to.
If you can’t identify a chord in the key, then leave it for now until you study non-diatonic chords in the next section.
Secondary Dominant Chords
As well as seeing diatonic chords when using Roman numerals for analysis, you’ll also see non-diatonic chords.
In this lesson we’ll look at two types of non-diatonic chords and how to analyze them with Roman numerals. These aren’t the only non-diatonic chords you’ll see when analyzing tunes, but they’re the most popular, so are essential to know.
The first non-diatonic chord is called a secondary dominant chord.
This is a V7 chord that isn’t the V7 of the key you’re in, such as V7 of V7, V7 of iim7, V7 of vim7, etc.
When writing secondary dominant chords, you can write them as V7/V7 or V7/iim7, if you like.
Or, you can use a shortcut such as II7 for V7/V7 or VI7 for V7/iim7, as both are commonly used in modern analysis.
I prefer to keep things close to the key, so I prefer II7 and VI7 for example, but try both and see which makes the most sense to you.
Here’s an example of a VI7 chord in the key of C major.
And here’s an example of a II7 chord in the key of C major.
Now that you know what secondary dominant chords are, grab a Real Book and identify secondary dominant chords in full tunes.
Secondary ii V Chords
As well as seeing secondary dominant chords, you also see secondary ii V chords in jazz progressions and tunes.
Secondary ii Vs function the same as secondary dominant chords, except you use a ii V leading to a diatonic chord rather than just a V7.
Here’s an example of a secondary ii V that leads to the iim7 in the key of C major, meaning Em7b5-A7b13 leading to Dm7.
Notice that the song doesn’t modulate to D minor, the secondary ii V is used to highlight the Dm7 chord, but not change to the full key of D minor.
Here’s another common example of a secondary ii V that Charlie Parker used a lot in his tunes.
In this example, the secondary ii V is used to highlight the vim7 chord (Am7), as well as acting as a transition bar between Imaj7 and vim7.
Now that you know what secondary ii V chords are, grab a fake book and identify secondary ii V chords in full tunes.
Take the A Train Analysis
Now that you know what Roman numerals are, and their common usage in jazz, you can look at them over an entire tune.
Here’s the chord progression to Take the A Train with Roman numerals below each chord in the tune.
Notice that I used the II7 rather than V7/V7 in bars 3 and 4 of the A section (D7). You can use either analysis, but I prefer to relate Roman numerals to the key if possible to make it easier to transpose later on if needed.
Check out these changes, it’s a very diatonic progression with the exception of the D7 (V7/V7 (II7)) and the Gm7-C7 (iim7/IV and V7/IV).
You can also use Roman numerals in minor keys, such as when analyzing and learning a song like Summertime, which is in D minor.
When using Roman numerals in minor keys all the same rules apply that you learned in major keys, with one exception.
Normally minor chords are written with a lowercase Roman numeral (iim7 for example), but in minor keys the tonic chord uses a capital letter (Im7). This is to signify that the tonic chord is special, it’s the resolution chord of the key, and therefore we use a capital letter to reflect that.
Here’s the Roman numeral analysis of Summertime.
Notice that there are three main chords in the song, Im7 (Dm7), ivm7 (Gm7), and Fmaj7 (bIIImaj7).
The rest of the chords are just ii V’s that lead to those chords, so one diatonic ii V and two secondary ii V chords.
Transposing With Roman Numerals
Besides using Roman numerals to analyze and understand chord progressions, you also use them to make transposing easier on and off the guitar.
Here’s the chord progression for the first A section of Take the A Train, in the original key with Roman numerals underneath.
Now, to transpose this progression to another key, we’ll use F major as an example, you just need to know the Roman numerals and notes in the new key.
The notes in the key of F are F G A Bb C D E F, so all you do is move the Roman numerals from C to F and you have the same progression in a new key.
Here are the chords in F, notice that the Roman numerals remain the same, but you’ve changed the chord symbols to be in the new key of F.
After you look at this example, see if you can write out the chords to the first A section of Take the A Train in other keys using the same approach.
Transposing chords on guitar is an essential skill to have, and Roman numerals make this skill easier to learn and quicker to apply in your playing.