If you have a song that is a Fifth-Up Progression like Jimi Hendrix Hey Joe where there is a chord progression of c g d a e. Why is it that you can use em for soloing and what other modulation and scales go with the chords of the progression?
I really don't understand why you have had so much trouble asking this question on this forum yesterday! It seems like a good question and gets into something that I think is particular to rock style.
Full disclosure: while I know the song, I never played it until yesterday and I had to fake it really badly.
But I was trying to understand the how and why and this is what I came up with:
First we have to make an important point about blues and rock tonality: a minor third added to a major chord is dissonant in traditional harmony terms, but very much in style for blues and rock. In fact, you could say it is definitive of the tonal style in blues and rock. For example, a
G natural can be added to a
E major chord which contains a
G#. Voicing is important. It's typical to have the minor third, the
G natural, in a high register in melodic passages.
Next, let's point out the chord do no get equal duration.
C G D A go over 8 beats and then
E alone gets 8 beats. Right from there we see
E gets more time and that reinforces
E as a stable goal, as the tonic.
Put these first two points together and we can see that 50% of the performance time is presenting a fundamental blues tonality. Half the time it's just straight forward blues.
What remains is a way to understand the portion that is
C G D A.
G chord is easily "explained." The relative minor of
E minor pentatonic is
G major pentatonic. It's the same set of tones just starting on
G instead of
E. Shift emphasis away from
A in the scale and it's all chord tones matching the
When comparing the remaining chords
C D A with
E minor pentatonic we see there is a fair amount of "agreement" between the chords and scale depending on how you look at it. Basically the scale provides two chord tones for each of those chords and all the other non-chord tones are sensible in terms of related keys.
Just to flesh that idea out a bit, imagine a lick alternating between
G. Both tones in it will match the
G chords. If we allow for the
A to take the form of a dominant seventh, then
E G matches that too. Image a lick alternating
D. Treating one as the neighbor tone of the other it will match any of the five chords in the whole progression.
That point is worth repeating. Licks focusing on
D will match any of the chords simply by shifting between one or the other as the chord tone.
But all this chord tone matching seems artificial. I don't think anyone thinks about that when they play in this style.
The thing that makes it "click "for me is to just play an
E on top of each chord. I did it strumming this:
C x32010 G 35x45x D xx0230 A x02220 E 022100
...when I did that I thought "oh, yeah, that's the basic sound of the song."
Technically, when you hold a tone over a series of chord changes it's called a pedal. In this case the pedal
E is the ostensible tonic, so it's called a tonic pedal. The important thing with a pedal is the deliberate clashing of tones as the chords move away from the pedal.
We can forget all the fussiness of trying to match chord tones to the
E minor pentatonic. The tonic is
E, the guitar solo remains firmly in
E minor pentatonic, and when the chords move through
C G D A it's a source of dynamic tension under the soloist driving to and reinforcing the
You could also break it up into two segments.
C is a tension resolving to
G matches the scale, then secondly
D A is a tension resolving to
E matching the scale.
Either way the point is: to the extent that the
A chord seem to not match the scale, it is not a problem. It is a dynamic force in the music. During the solo
E minor pentatonic is the foundation. The chords dynamically support that tonic.
If you don't mind mixing music theory with your rock, you might want to read this:
The fifths-up bass movement doesn't have anything to do with the suitability of the pentatonic scale per se. Even if there are many chords, there are two main keys. The progression is sliding between G major (E minor) and E major keys and letting you wander somewhere in between, and E minor pentatonic notes just happen to do something sensible in both G major and E major. Layering E minor pentatonic or E minor blues over E major is a common bluesy trick. Play X minor pentatonic scale over X major key. Flirt with major/minor mode changes.
Exactly when does the key change? All the time? Never? It's up to you to decide. Here are a few possible ways to interpret and handle the harmony:
If we remove all of the harmonic ambiguity and "guess what the key is" tricks from blues and jazz, the song might become something like this:
The Hey Joe progression has been talked about in this question Chord progression if the chords are not part of the scale?
The accepted answer analyses it as a series of I - V motions and key changes along the circle of fifths, but to me that feels like a far-fetched solution. To my ear, the most natural way to hear the chords is IV - I - V - II in the key of G, and then the E major - and perhaps the preceding A major is the only real "surprise" with a touch of key change feeling, because E minor was expected there. Removing those mode change feelings it becomes:
C G D Am Em
But it's just been jazzed up a bit by changing the Am and Em to majors. As the OP noticed, you can play E minor pentatonic over the entire progression, and it kind of glues it with a feeling of being in Em all the time.