Pentatonic Harmony

Rock music, and popular music more generally, owes a great debt to the blues tradition. One of the most pervasive pitch collections in pop and rock music is the pentatonic collection, a five-note collection also firmly rooted in the blues.

Basic Scale Materials

The pentatonic scale is related to the blues scale and the diatonic scale: it is a subset of both of those collections that is distinctive for containing only 5 pitches and no semitones. As a 5-pitch collection, there are 5 different rotations of the pentatonic collection (just like there are 7 rotations of the diatonic). In this case (unlikely some 5-note collections) all 5 rotations are different from each other.^[1] In popular music, the pentatonic scale is typically found in one of two rotations: the “major pentatonic” and the “minor pentatonic” scales. Example 1 shows these two main rotations (on the top stave) and then all 5 (on the bottom).^[2]

Example 1. Pentatonic scales.

“Scale Degree conflict” a.k.a. “Cross Relations”

In rock music, a harmonic system based on the pentatonic scale is typically created by using the scale as chord roots. The chords can be major triads, minor triads, power chords (chords with a root and fifth but no third), or anything else (including sevenths, added notes etc.). Note that this flexibility in terms of the chord “quality” means that the total pitch collection is often not exclusively pentatonic: often, the chord tones combine to make a collection that doesn’t correspond to the pentatonic, or even any of the 7-note modes we’ve encountered so far.

Example 2 shows how this can be understood in terms of a “conflict” or “cross relation” between scale degrees.^[3] Both staves show major triads built on the notes of the pentatonic scale.

• The first collection (upper stave) is built on the pentatonic in “rotation 1” and includes:
  • ti and te [latex](\hat7, \downarrow\hat7)[/latex] colored blue);
• The second collection (lower stave) builds on pentatonic “rotation 4”. It includes both
  • mi and me [latex](\hat3, \downarrow\hat3)[/latex], colored blue) and also
  • la and le [latex](\hat6, \downarrow\hat6)[/latex] (colored purple).

Example 2. Pentatonic harmony derived from two different rotations of the pentatonic scale.

“Scale Degree” / “Cross Relation” conflict through parallel triads

Example 2 shows major triads on pentatonic scale degrees specifically. This is quite a common example of how cross-relations arise in popular music chord cycles. Nicole Biamonte and others have noted that its probably not a coincidence this fits so well on the guitar: melodies and chord roots based on the pentatonic, with parallel (“barre”) chords that are all major.^[4]

Example 3 shows an excerpt from “Higher Ground” by Stevie Wonder (1973), in which the pervasive harmonic loop can be understood as derived from the pentatonic scale. Note that the while first chord quality is somewhat ambiguous (arguably at least based on parallel major triads with or without added tones), the bass is perfectly clear.

Example 3. Stevie Wonder, “Higher Ground” (1973).

Fifths and Fifth Progressions in light of the Pentatonic

The pentatonic collection is a subset of the diatonic collection and both have the notable property that they can be constructed by successive fifths. For example:

• the diatonic collection can be built from hey succession of fifths like F-C-G-D-A-E-B (in order: C-D-E-F-G-A-B), and
• the pentatonic collection can be formed from the central five of these: C-G-D-A-E (in order: C-D-E-G-A).

That being the case, chord progressions like the cycle of fifths can feature in the pentatonic case, or at least part of that cycle can. Likewise, other chord progressions organised around fifths can be understood in terms of the pentatonic.

For example, successive pairs of fifths a tone apart give progressions like:^[5]

• D-A, C-G, …
• G-C, A-D, …

The first of these (D-A-C-G) is the chord progression of TLC’s hit song Waterfalls (1994/5). Once again, we can keep the quality of the chord (major, minor, …) separate from the bass here.

As so often, the distinction between different categories gets complicated. For example, we could also view this view this D-A-C-G progression in terms of Double plagal Mixolydian schema  (♭VII–IV–I), but with a V, so I–V–♭VII–IV–(I). So if this progression could be pentatonic and/or mixolydian, what really makes a quintessential pentatonic progression.^[6]

Quintessential Pentatonic?

• most of the progressions we’ve seen have fewer than five chords in them (they’re a “subset” of the full collection, whether modal, pentatonic or anything else),
• the quality of those chords and the overall pitch content are quite flexible.

There’s no easy answer – many progressions could be described in terms of either pentatonic or other modes. And that clarity (or otherwise) is related to many factors. For example, if the tonic/final is not clear and we consider only the notes, then all pentatonic progressions are subsets of all diatonic modes because the pentatonic collection is a subset of the diatonic. Usually though we have some sense of the tonic/final and can narrow it down to ambiguities like “minor pentatonic or aeolian subset.”^[7] This question (and possible answers) are also related to considerations other than chords: how does the main melody work?, what about any improvised solos?, and (crucially) what is the style/genre context?

Are there any progressions with all five notes of the pentatonic? Why yes, there (occasionally) are. Let’s close by considering an example of a 5-chord pentatonic progression that also draws together many of the topics discussed above.

Hey Joe, where you going with that progression of fourths?

“Hey Joe” has been performed and recorded by countless artists, probably most famously by Jimi Hendrix and the Jimi Hendrix Experience.^[8]

The (main) chord progression is a sequence of five chords, with the interval of a descending 4ths (or rising fifth) between each, that ends on the tonic. Example 3 shows this progression with a tonic root of E (as is the case in the Hendrix version, 1966). The scale degree conflicts are highlighted as they were above:

• mi and me [latex](\hat3, \downarrow\hat3)[/latex], colored blue) and also
• la and le [latex](\hat6, \downarrow\hat6)[/latex] (colored purple).

Example 3. “Hey Joe”, chord progression, e.g., as recorded by Jimi Hendrix, (1966).

Biamonte (2010) includes this example, noting the chain of fourths, and seeing this kind of progression in terms of pentatonic mode in rotation 4 (look back to Examples 1 & 2). Pentatonic rotation 4 seems to be relatively common and it also seems to attract longer chord chains (include 5) than other rotations and contexts do (where 2–4 is typical).^[9]

In any case, a full 5-chord progression hitting all and only the notes of the pentatonic makes a pretty strong case for a pentatonic reading. But even here, it’s ambiguous. This pentatonic rotation is a subset of several diatonic modes, including the Aeolian (without [latex]\hat2, \hat5[/latex]). And this progression of descending fourths could be heard, once again, in terms of an extended version of the Double plagal – now a “quintuple plagal” perhaps? – which we first encountered in terms of the mixolydian. In that reading, the double plagal (♭VII–IV–I) is now extended as shown on Example 3 (♭VI–♭III–♭VII–IV–I).

All we can advise is to practice analysing parts separately and combine them freely. In encountering a new piece, you might ask:

• what is the overall tonic?
• what are the chord roots ?
• what is the pitch collection in the chords overall (i.e., not only the roots)?
• what is the pitch collection in the piece overall (i.e., not only the chords)?

Having considered those questions separately, you’re well placed to consider combining them:

• do the chord roots and the overall tonic combine to suggest a mode (whether pentatonic or aeolian, etc.)?
• do the rest of the chord tones fit this or suggest some other origin like parallel writing?
• does the rest of the pitch content fit or not?
• how does all of this relate to other pieces you know and wider questions of style/genre?

Finally, don’t feel the need to come up with categorical, comprehensive answers every time: you can recognise the case for both pentatonic and Aeolian, and view those readings as equal, or come down in favor of one while still recognizing the other.

• Biamonte, Nicole. 2010. “Triadic Modal and Pentatonic Patterns in Rock Music.” Music Theory Spectrum 32 (2): 95–110. https://doi.org/10.1525/mts.2010.32.2.95.
• Lewandowski, Stephan. 2010. »›Fallende Quintanstiege‹. Ein Modellversuch«, Zeitschrift der Gesellschaft für Musiktheorie 7/1, 85–97. https://doi.org/10.31751/508
• Spicer, Mark. 2017. “Fragile, Emergent, and Absent Tonics in Pop and Rock Songs.” Music Theory Online 23 (2). http://mtosmt.org/issues/mto.17.23.2/mto.17.23.2.spicer.html.
• Tagg, Philip. 2011. Everyday Tonality: Towards a Tonal Theory of What Most People Hear. 1.3. New York: The Mass Media Music Scholars’ Press.

1. Coming soon!