I felt good that I was learning all my KEYS (chords and their relative minors).  It seemed to open up my understanding of things- I was hearing songs as I practiced my I, IV, V's BUT, as I began to explore I started noticing that many songs don't follow a KEY- they may be related via modes and other scales but not in keeping with the Major scales.  My take away so far is it's Rock n Roll so if it sounds good, go for it.  If it resolves back to the tonic chord you can usually get away with it.  Tell me if I am wrong.  Two examples that come to mind.  Perl Jam- Alive.  The chorus is E, G, A- over that, I can solo in Em Pentatonic and it sounds perfect- yet, G and D are not in the key of E.  It shares only E and A.  My second example, is when I play Blues, e.g., A, the add the C, then D power-chords, it just sounds and feel right but A, C and D are not in any given scale.  If you play powerchords, perfect fifths going up the fret board, they sound great together but don't necessarily fit any given key.  The more I learn, the more I realize how v e r y little I know.  
The songs are still in a key. All songs are in a key (or several if they have key changes) unless they are atonal. Songs just commonly use "outside" chords to create additional coloring in chord progressions. It's very common to use minor pentatonic scales over the relative major. It's also very common to play minor key-esque progressions (i-bIII-IV or bVI-bVII-i) but replacing the major chords with minors (in those cases the i chord could become a major). My favorite is the Super Mario Bros progression, which goes IV-V-bVI-bVII-I.

The thing to remember is that a key has to do with resolution and tonal center. A song in Dm but with a natural 6th (and therefore no accidentals) is still the key of Dm so long as it resolves to a Dm chord. Despite using a Dorian scale it would be erroneous to describe the song as being in the key of D Dorian. It's just Dm with the use of a natural 6th throughout the piece, which is very common in Irish music for example where minor keys almost always use a natural 6th. But it still resolveson a Dm chord.

The important thing to remember about music theory is that it is descriptive rather than prescriptive. Music theory is all about observations and nomenclature that makes it easier to analyze, describe, and communicate musical ideas rather than a set of rules that have to be followed. A lot of people get tripped up on this since they look at "wrong" notes and feel that music theory wouldn't "allow" such a thing when really the outside notes are perfectly acceptable if they fit in context or give the sound you want, and music theory can describe what is going on but it doesn't tell you what you have to do.
There's no such thing; there never was. Where I am going you cannot follow me now.
theogonia777 Thanks Kristen- well said and great points.- very helpful. I'm trying to use the theory as a general framework to help guide and actually increase creativity. It can get very complicated but I never forget that some of the best players know very little theory- it's about feel, flexibility, patterns, etc.  Sprinkling a little theory is super useful as it unlocks doors and helps me to better understand what it is that I am actually doing/playing.  Having studied in my downtime last month I played the same things I have been playing for years but actually was able to connect some dots and improvise and solo over it because I knew where I was in the general frame.  I also bought an updated pedal and learned about looping- which is a lot of fun.  Playing a long with songs in key is also great.  I am realizing that soloing is not necessarily as important as rhythm and song structure- it is simply a nice compliment to an arrangement.  With rare exception, a song can live without a solo/lead but it can't really exist without the rhythm.  When considered along those lines, I am able to relax more and enjoy playing along- rather than worry thinking that I have to hit every note perfectly.  I realize that some of the best notes I hit are notes I never play- it's the confidence to be quiet- to pause, to build and syncopate in time in order to really accentuate and compliment any given piece.  I have so much to learn but it's a fun journey with no final destination- just new adventures.  Thanks again for providing more pieces to this music puzzle- great forum!
Defined narrowly, the Key only tells you a single note: the one your A section resolves to. Everything beyond that is part of the journey away from and back to the tonic. You can put literally anything in between. I can't tell you how many jazz songs start with something Bb G7/B C-7, going "out of key" on the second chord.

A term you may find useful is Diatonic. It means "according to the key", and refers to anything that's contained entirely within the key signature's notes. Diatonic chord progressions are progressions that use only in-key notes.

Thus what you're asking about is non-diatonic harmony. That is, harmonies with notes not in the key signature. Just about anything blues-based is going to be non-diatonic in some aspect.

You've already made good observations, seeing the relationship between the major key and the chords being borrowed from the parallel minor. Your question is on point. Keep it up.

Just please don't use power chords when you're playing the blues.
Thanks cdg.  I learned 12 bar blues in Em by my Berkeley grad instructor.  I believe the correct third chord is a power chord or fifth- B I believe.  To make that shape, I just go up two frets and down one.  I usually add my pinky up higher to add more sounds but it's yet another power chord- unless I'm calling it the wrong thing.  I thought the classic and timeless sound of most blues rhythms where based off almost always off of simple power chord strumming progressions (1 & 2 & 3 & 4 &...) with simple pentatonic improvisations over the top.  E.g., Johnny Be Good, at A, etc...
Kristen nailed it pretty well. Take a song like the Beach Boys "Warmth of the Sun". It's in the key of C but the chords wander off in ways you would never expect if you only thought of chords generally in C. It also seamlessly jumps keys to A and manages to resolve back to the key of C. Awesome writing!!

C.......Am.......Eb........Cm.........Dm7.........G.......G+       Strange and beautiful.


Yes I am guitarded also, nice to meet you.
Last edited by Rickholly74 at May 29, 2017,
Music theory doesn't explain the music exactly, it's just a map that is used to navigate the music. Some people just use their ears, some people like something they can wrap their intellect around.