[No, I’m not dead yet — just absolutely snowed under in my day job. Here is a little blog post to keep the blog alive.]
Anybody who has ever played off a jazz lead sheet or ‘fake book’ is familiar with chord symbols like G (G major triad), Cm (C minor triad), D7 (D dominant seventh), G/D (G major triad with a D in the bass), and the like.
One ‘abstraction level’ above is the so-called ‘Roman numeral analysis’ which is found in music theory texts, particularly classical ones. It considers not the absolute chords but their relative position (and diatonic function) in the scale. For example, a 12-bar major blues in G corresponds to the progression G-C-G-D-C , and in C# to C#-F#-C#-G#-F#, but in Roman numeral notation, both would be I-I-IV-I-V-IV in their respective keys. Likewise, a minor blues would be i-i-iv-i-v-iv regardless of the key it is in.[*]
The system was invented by the eccentric classicist composer and music theoretician https://en.wikipedia.org/wiki/Georg_Joseph_Vogler (teacher of Carl Maria von Weber) in the late 1700s. It is not a system that comes naturally to people with absolute pitch (since the same progression in different keys really sounds different to us) but it is an excellent ‘meta’ tool for describing commonalities between what may be very different compositions. Effectively, it is a form of notation that stresses function (as in ‘functional harmony’) — tonic (I), mediant (III), subdominant (IV), dominant (V), etc.
As already seen in the blues example above, major chords are indicated by uppercase Roman numerals, and minor chords by lowercase ones. Seventh, ninth,… chords take digit qualifiers just like in conventional chord notation, e.g., i9, Vb9, etc. A ‘+’ and a ‘°’ indicate augmented and diminished chords, respectively.
Inversions are indicated by suffixes like Ib (tonic, 2nd inversion) and V7d (dominant, third inversion) although I personally find the ‘b’ confusing due to its similarity to a ‘flat’ sign and prefer I/V and V7/IV, respectively. (In C major, these would correspond to C/G and G7/F, respectively)
Finally, out-of-scale chords are prefixed by accidentals # and ♭. For example, a Neapolitan chord in a piece otherwise in a minor scale would be written♭II
Rick Beato has a video here about ‘the four chords that killed pop music’.
What he really means is the progression I-vi-IV-V and its permutations like vi-IV-I-V, which some producers seem to think are nearly a prerequisite for hit singles. In Rick’s video, you can hear a plethora of examples in a wide variety of keys and styles (what do Taylor Swift and Iron Maiden otherwise have in common?! Or the choruses of Roxette’s ‘Listen To Your Heart’ and The Beatles’s ‘Let It Be’?). At a higher abstraction level, all of them boil down to just that pattern I-vi-IV-V, straight up or rearranged.
To be sure, if one is willing to escape the tyranny of simple triads and power chords, even I-vi-IV-V can be made interesting… And if one is not (e.g., because on a distorted guitar more complex chords quickly get muddy), then changing the scale to a more exotic one helps…
For instance, here is a video touting the Mixolydian mode as the ‘secret sauce’ of AC/DC
Leaving aside that AC/DC, while fun to play, is hardly a model of musical sophistication: What is he talking about? Let’s compare the diatonic triads on the major scale with those on the Mixolydian scale (more correctly: the Mixolydian mode[*]):
major (Ionian): I – ii – iii – IV – V – vi – vii°
Mixolydian: I – ii – iii° – IV – v – vi – VII
Yes, the major triads in the major scale are the familiar tonic, subdominant, and dominant — but the mixolydian one has them on tonic, subdominant, and leading tone! This automatically invites riffs like A-A-A….D-D-G…D-D-G-D-D-G-D-A-A (“Highway To Hell”) or E–D-A/C# (“Back In Black”), or …
They also use the Dorian mode fairly freely (“Hells’ Bells”, “Shot Down In Flames”,..)
Dorian: i – ii – ♭III – IV – v – vi° – VII
Now the Mixolydian and Dorian modes are, of course, very common in Anglo(-American) folk music — but yes, much of the character of different scales and modes derives from the chords progressions they generate. I will elaborate in this in a future post. Meanwhile, here are the biting observations of one of my musical heroes, Steven Wilson, on the music industry:
[*] The “Nashville number system” used by some country and gospel singers (including by Elvis Presley’s backup singers the Jordanaires) is a variant that uses Arabic instead of Roman numerals, with minor chords being indicated by a dash (e.g. 6- instead of vi). It was invented to facilitate transposition to fit the vocal range of the singer being accompanied.
[**] Technically, a scale is a sequence of notes/intervals covering an octave, a mode a different choice of tonal center (‘starting point’) among them. For example, the G mixolydian mode is generated from the C major scale simply by starting at G rather than C.