tldr: Hey Joe is a blues-based song in E major. The intro and lead work primarily uses the E minor pentatonic scale. The chord progression is C-G-D-A-E, which progresses by following the circle of fourths/fifths from one chord to the next (each chord’s root is a fourth above, and a fifth below, the subsequent chord’s root). The final two chords are diatonic — the A and E are the IV and I in key — but the C, G, and D are bVI, bIII, and bVII chords borrowed from the parallel minor key, E minor.
Hey Joe analysis
Poking around on the Web, it looks like a common harmonic analysis for this song is “it works because it’s a circle of fifths progression.” While that is true, I think there’s a bit more to it.
First, Hey Joe is a blues-based song in E major. By that I mean that the song is in a major key, but incorporates the parallel minor scale, and particularly its minor third, which is a hallmark of the blues. Every lead part in the song employs the E minor pentatonic scale, which is exactly what one would expect in such a context. The intro riff sets the scene by following the minor pentatonic pattern to step downward from the high E string to the low E open chord. First, a slide from fret 3 to 5 back to 3 on the B string (playing the open high E string with it), then a slide from 4 to 2 pulling off to 0 on the G string (playing the now-open B string with it), then the E notes on the D string (fret 2) and low E string (0), expanding to an open E major chord. That resolution makes clear that the E is the tonic and E major the key. He also adds in a harmonized flat 3 counterpoint (x55xxx – x44xxx – 022100) and an E minor pentatonic flourish around the E chord at the 7th fret.
The magic happens with the central progression that is repeated through the song: C – G – D – A – E. Play from the third fret and you can see the circle-of-fifths progression, or more specifically, a circle-of-fourths progression:
-3--3--5--5--7------- -5--3--7--5--9------- -5--4--7--6--9------- -5--5--7--7--9------- -3--x--5--x--7------- ----3-----5----------
*Note that the chords with the “x” here are standard E-shaped barre chords, but played with the thumb holding down the low E string fret, muting the x string with either the thumb, the tip of your ring finger, or both, depending on your hand. That’s how Hendrix played them, and it leaves your pinky free to add flourishes off of the chord.
What “circle of fourths progression” means is, starting from the C chord, the next chord is reached by going down by an interval of a perfect fourth to G, then down a perfect fourth (or up a fifth) from G to D, then down a perfect fourth to A, then down a perfect fourth (or up a fifth) to E. Just look at the roots (bolded) and you’ll see the pattern. The reason that this could be viewed as fourths or fifths is that they are two sides of the same coin: going up a fifth leads to the same note as going down a fourth and vice versa.
The “circle of fifths” and its mirror image the “circle of fourths” is the pattern that emerges following this principle, going through all 12 notes/keys before returning to where you started. Do a Google search and you’ll see the circle image that shows it visually. There are a number of uses and implications for this, among which is that chord progressions often move in one direction by fourths/fifths because it sounds great. While the pattern is a mathematical consequence of the distribution of notes, there are a couple of reasons it sounds great. First is just the logical nature of the pattern, moving the same distance each time. And if you use all major chords or all minor chords, every note in the chord is going the same distance of a fifth each time. Second is that you end up easing between chords through shared and adjacent notes. Taking the progression in Hey Joe as an example, the C chord is C – E – G. The G chord is G – B – D. As you can see, the fifth of the first chord (G) becomes the root of the following chord. Also, the root of the first chord is adjacent to the major third of the second (here, C and B), creating a chromatic leading quality between the two. If you use minor chords instead of major, you lose the adjacent root of the first chord and major third of the second, but you pick up a different adjacent note. Flattening the third of the first chord (Eb in the Cm chord) makes it adjacent to the fifth of the following chord (D in G major or minor).
Tangent paragraph: Relatedly, though not really used in Hey Joe, you can also follow what is called a diatonic circle of fifths, which is an application of it using only the fourths/fifths within a particular key and scale. Taking the major scale, all of the notes can be arranged by perfect fourths/fifths except the 7th note: it is a diminished fifth (a half step down from a fifth) distance up, and an augmented fifth distance down, from the 4th degree of the scale. So instead of using the perfect fifth that you find in the chromatic circle of fifths, you use the diminished one within the scale. Taking C major as an example, and using the diatonic notes of the key to establish the quality of the chords (major or minor), you can neatly progress through all of the diatonic chords in the key as follows: C – F – Bø – Em – Am – Dm – G – C, which is I – IV – viiø – iii – vi – ii – V – I. By contrast, a perfect fourth up from F in the chromatic circle of fifths would have been Bb, which would have changed everything after the second chord in the series.
So, we can see that Hey Joe follows a chromatic circle of fifths pattern, in that the chords are all major chords (whereas a diatonic circle pattern would have some minor chords mixed in too) and because there’s a D chord, whereas the diatonic vii chord in E major would be D#ø. But that only tells us half of the story, because in theory such a progression could start or end on any chord, even ones completely unrelated to the key.
What’s happening here is that Hey Joe cleverly uses the chromatic circle pattern to transition between diatonic chords of the E major key and chords that are borrowed from E minor. The first three chords in the progression, C, G, and D, are the major chords from the key of E minor, characterized as bVI, bIII, and bVII chords. Just as you can borrow chords from any parallel key/scale, this song borrows these from the parallel E minor. This fits particularly well in the blues context, which is already based on the concept of mixing major with minor. Then, taking advantage of the natural progression of that circle pattern to A, which is the diatonic IV chord of E major, it returns us nicely to the E major tonic chord.
Finally, while most of his lead work is using the E minor pentatonic scale, Hendrix near the end does a chromatic pattern based around the roots of the chords of the progression (bolded):
---------------------------------7- ---------------------------------9- ---------------------------------9- ---------------------------------9- -3---------2-3-4-5---------4-5-6-7- ---0-1-2-3---------2-3-4-5---------