Whats the deal with this?? (for you theorists)

It's just a simple "key of the moment" progression.

C is the starting tone, then . . .
G is the 5 of C, then . . .
D is the 5 of G, then . . .
A is the 5 of D, then . . .
E is the 5 of A

Now going back to C is the flat-6 of E, so it provides a little dissonance, but not too much since you're going to the 5 of C immediately.

wow, that's simpler than I thought, so what makes the song in the key of E then??

The key signature for the melody

Ah.

Is this what people are talking about when they talk about the "CAGED system/method"?

I understand that, but what I mean is, why is it in the key of E if it has C-G-D-A-E in it, couldn't it be just as easily in another key such as G? I guess my question is what exactly makes it in this key. Because it only has 2 chords that appear in a traditional E major key (being E and A).

Well... this type of progression is called a 'circle progression' because it follows the circle of fifths. If you look at the keynotes of the chords, it's pretty clear what 'key' you're in, too... there are no chords that contain sharps, and there's one chord (C) with no accidentals in the key. So it's in the key of C* - which contains every chord's keynote (C, D, E, G, A).

*The song can also be written in G, since there's no F chord, and no F note in the C chord. But that's not as good a choice as C, sincee there would be no tonic chord.

So why does it work?

That's fairly simple too - each chord is a fifth higher than the one before it. So it's moving around the circle of fifths. Although a typical chord progression moves the other way, in fourths (like the natural harmonic series, viiº-iii-vi-ii-V-I), fifths are just inverted fourths, and it sounds fine. We hear movement by fourth/fifth in just about every song we play!

So what's confusing is the fact that we have all major chords here.

You can always substitute a major chord for a minor one, or vice versa - that's called borrowing from the parallel key. It'll sound a little dischordant, since some notes will be 'out of key', but it won't be jarringly so - look at the tune "Dock of the Bay" and you'll see a song that uses seven major chords - one for each step of the diatonic scale (which determines the key of the song)

I am not a theory guy whatsover, so take this with a grain of salt. I think what establishes this song in the key of E is because it is the last chord in the progression. This gives the progression a feeling of finality. Also, all other chords are played for two beats, while the final E chord is played for two full measures.

Really, you probably could play the solo in C, G, D, or A and it would work. But this song, at least the Hendrix version the solo is primarily played in the E Minor Pentatonic scale.

I don't think looking at the chord the piece ends in is that great of a way of determining key. It probably works more often for rock/pop music, but with classical compositions, there are pieces of music that don't end with the exact chord that represents the key that it is in -- a Picardi third is used, for example, in which the piece ends in the major tonic, when in fact, the piece is in a minor key

I didn't mean that this song is in E simply because it ends in E. No, this song is simply following the cycle of fifths. C to G, G to D, D to A, then A to E. This could go on forever. You could go to B, then F#, then C#....

But it doesn't. It stops on the E chord. And this chord is given emphasis by being played for two full measures where all other chords are played two beats only and quickly go to the next fifth.

In a sense, this song is not in any key as long as it continues to go to the next fifth. It is only because it finally stops on the E that it gives the listener a sense of the key.

Well the final chord is all about cadences.

Classical music uses a wider variety of cadences than pop/rock. In pop/rock it's most common to find the piece ends on coming back to the first or root chord (unless it just finishes on the final chord of its regular progression). This will give it a complete feel. If you finish in a different key or not on the root/I chord then it leaves it open and people think the piece is unresolved and it's kindof like a cliff hanger.

Cadences are a pretty good way to really imprint a feel of the song into the listener's mind.

Sorry to ramble on...

As I wrote earlier, I know little about theory. But I have ears.

Try this progression and stop anywhere you choose. Go C, G, D, and then play the A chord two measures. The song will sound the key of A. Try it and see.

Haha.

Unfortunately this is where theory over-rules ears!

What your ears are hearing is you finishing on a major chord. Finishing on major chords gives the impression that every thing is complete.

Now if you play the same 4 chords but an Am instead of an A. Whenever you feel like it, finish on the Am. You'll notice that your mind is waiting for that next major chord to complete the piece.

You finished on Am. First of all this is definitely not the key the piece is in and second of all you can't finish on an Am playing those chords without it sounding incomplete.

Therefore you require theory.

I hope I explained well enough, it's 3:30am over here!

I am sure you are correct about the theory. But I just played the progression you suggested and it gave the song a feeling of being in A minor. I played a little solo with the A minor pentatonic and sounded just fine, and the correct scale to use.

Once again I have failed.

D'oh! :o

Am is the relative minor key to C (Am, C, Em, G, F all sound good together) so that's why it sounds good.

I'll come back to you later as to why such is such.