The Architecture of Music


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Roman Numeral Analysis

By Ethan Lustig, MA Music Theory

Just as each mode of a scale gets its own roman numeral conveying the scale degree that it starts on, we can also name each triad by referring to the scale degree that serves as its root. So in A Dorian, C maj3 (C E G) is simply called III because its root is C, which is the third scale degree of the A Dorian scale. Similarly, G maj3 (G B D) is called VII. If we move to the Ionian mode (mode VII) of A Dorian, this changes the sound of the song because the tonic/key note has changed (it is now G instead of A); however, the background pitch collection of the master scale, mode I (the A Dorian scale) has not changed, and so the roman numerals that we assign to each triad remain the same: C maj3 (C E G) is still called III, and G maj3 (G B D) is still called VII.

On the other hand, if we were to change the master scale’s key note itself, then the roman numerals of each triad would change (as would the scale degrees and the pitch collection). So, the roman numeral that you assign to a triad depends on the context; that is, it depends on the master scale’s key note. For instance, if we move to the D Dorian scale instead of A Dorian, then C Maj3 (C E G) is no longer called III: now it is called VII, because its root (C) is mode VII of D Dorian. And G maj3 (G B D) would now be called IV instead of VII.

Unlike the roman numerals for scale degrees, which are always uppercase, further detail is added to the roman numerals for triads, by using uppercase and lowercase to distinguish between maj3 (4 3 5) triads and min3 (3 4 5) triads, respectively. So, in A Dorian, A min3 (A C E) would be called i, not I; and B min3 (B D F#) is ii, not II. You can use a ˚ sign to show diminished triads (3 3 6). In Dorian, there is one diminished triad, which is built on scale degree VI; we call that triad vi˚. (In A Dorian, vi˚ would be F# diminished [F# A C]).

Approaching and listening to chord progressions as roman numerals is powerful because it is an abstraction that lets you generalize, finding the chords and chord successions that you like best. It is much easier and more meaningful to think about a progression as (for instance) i III IV i, rather than thinking about it as ACE-CEG-DF#A-ACE. And no matter what mode of the scale you are using as the tonic, the roman numerals remain the same. Just as the tonic pitch is the most stable pitch in a melody, the tonic chord is the most stable chord in a progression. Often, a piece in D Dorian (mode I) will end on its tonic, a i chord (D min3 or D F A). A piece in mode II of D Dorian will likely end on its tonic, a ii chord (E min3 or E G B).

Dorian Modes Triads

What about first inversion triads, second inversion triads, or triads with an add note? Well, everything above still applies. A maj3/1 (A C F) is still III in the D Dorian scale, and D maj3/2 (D G B) is still IV, because their roots (F and G respectively) have not changed. Inverted chords are useful because you can change up the sound by using variety, instead of only using root-position chords. Add notes can often be considered “non-essential” notes that add color and spice to a triad, and they don’t always need to belong to the scale. Even if you have some add notes that are outside of your scale, your song can still be clearly in a given scale and a tonality, as long as the triads fit the scale.

It can take some time to wrap your head around all these concepts, and they are best learned by playing around, listening, and playing around some more. The most important idea to remember here is that changing between modes of the same scale will change the tonic/key note, but it will not change the available pitches in the collection, nor the way we name the chords. Meanwhile, using the same scale, but in a different key, will keep the same general sound (because the interval formula does not fundamentally change), but will shift the available pitches in your collection; and the tonic/key note, as well as the roman numeral assigned to a triad of specific notes, will change.

Note: if you have encountered roman numeral analysis of chords in the past, you probably learned that they are based on the tonic, such that the roman numerals change for every mode and the tonic is always mode I. By this logic, C maj3 (C E G) would be VII in D Dorian, III in A Aeolian (Minor), and VI in E Phrygian (see page 253). The problem with this approach is that there are, needlessly, 7 times as many sets of roman numerals to keep track of! Instead, this book answers to the governing scale, the master of its modes. This method is far simpler, letting C maj3 (C E G) remain VII regardless of the tonic/key note of the mode being used with the D Dorian scale.

It is only when you actually change pitch collections—either by moving to another key note for the master scale itself (eg. moving from the D Dorian scale to the G Dorian scale), or by preserving the master scale’s key note but using a different scale entirely (eg. moving from the D Dorian scale to the D Mixo-Aeolian scale)—that the roman numerals of a specific triad of pitches change. However, using this book’s methodology, with the Dorian scale i, ii, and v will always be minor, and III, IV, and VII will always be major regardless of the key of the scale and the notes being used (see above). The scale degree of the modes also always stays consistent using this method: I is always Dorian, V is always Aeolian (Minor), VII is always Ionian (Major), and so on.