I've really progressed since I learned about your lessons - thank you so much.
I have recently heard Mark Knopfler's beautiful solo over "Knockin' on Heavens Door" (just after 2:08 in the video).
What puzzled me was that in his solo over the C chord he plays the note F.
Now I learned from you that it is either possible to play the scale of the key i.e. G in this song or to play over the arpeggios of the chords played.
In relation to G scale F would imply Mixolydian and in relation to the C chord - F is the 4th, so why does the note F fit in so beautifully?
Could it be that if the chord like in this song is played for a fairly long time it is also possible to play the scale of the chord i.e. C scale in our case? That would be something totally new for me.
If that were the case then it is also possible to play A minor scale and not A Dorian over the A minor chord of this song.
I'm really looking forward to your help on this one!
A Mere Glimpse of Another Scale
Dave, this is very interesting, thanks for sharing this example.
That F note kinda sticks out doesn't it?
To the casual listener, it might stick out as an "intriguing sound".
To a musician versed in the theory behind scales and chords, it sticks out as a non-diatonic or "outside" note.
Of course, outside just means it's not part of the key signature implied by the sequence of chords (G major - I V ii, I V IV).
Anyway, you're right Dave that when Knopfler plays that F note, he is effectively moving from G major/Ionian into G Mixolydian - a parallel shift.
Or you could look at it as him moving from G Ionian over Gmaj and Dmaj to C Ionian over Cmaj.
That's just two ways of seeing the same scale shift.
Now, why does it work?
Partly because F is a defining note in G Mixolydian harmony, as the b7, and this "carries over" to any other related chords (e.g. Cmaj, as the IV chord of G Mixolydian) because the ear is relating it to that G key centre.
I'm sure if you delve deep enough there'll be some physics behind why this works, but that's not my remit ;)
However, in a more general sense, it's about the note's role in a larger phrase.
When the 4th of a major chord is played, you can be 90% certain it will be preceded or proceeded by its neighbouring major 3rd - a very strong chord tone.
The perfect 4th and major 3rd, a semitone apart, have a strong relationship, because of a natural voice leading effect.
The 4th creates a pull to the major 3rd in most cases.
The 4th and 3rd complement each other over major chords, in other words.
In fact, even though it sounds like the 4th is what's creating the cool sound, it's the context in which it's used (interplay with the 3rd) that makes it what it is.
Notice how Knopfler doesn't hold the 4th. He resolves it immediately back to the major 3rd and continues his phrase.
The 4th is therefore a mere glimpse outside the G major scale, supported by the major 3rd of Cmaj.
But that glimpse was of one magnificent view, wasn't it?
Now, it's all very well being able to explain why something works, but you have to be able to hear it.
Many great players don't think so dogmatically about what specific scales or notes they're playing - they just explore options and add what sounds good to their repertoire of ideas.
So while it's useful to know scales and how they relate to different chords for a roadmap, you have to hear and feel what you play as a pure expression.
Changing Scales Over Diatonic Progressions
Of course, when starting out, it's best to keep it simple and think in terms of: "ok, this is a straightforward G major progression - I'll play G major/pentatonic".
But, once comfortable with diatonics, I always encourage players to break the "rules" occasionally, and venture outside into other scales.
The easiest way to think of this is playing a different scale on the root of a chord in the progression.
Knopfler essentially implied C Ionian over the Cmaj IV chord.
Slash played the G minor pentatonic blues scale over the entire progression in part of his rendition with Guns n Roses. It worked because I V IV is essentially a blues progression, so guitarists with a background in blues will approach these chords in a blues context.
You could also play C Mixolydian over the Cmaj IV chord (this would translate to G Dorian). This is a common variation in country music.
However, sometimes the chord in questions is so deeply attached to its parent scale (like a clingy child!) that it's difficult to find outside notes/scales that work.
For example, over the ii chord (Am) natural minor doesn't sound that great to my ears - the b6 of the scale (the note F in our example) just makes it sound awkward.
You really just have to experiment with different scales/notes over each chord if you want to venture outside the parent scale (G major in this case).
I'm sure when Knopfler first played the 4th over a IV chord, he knew he had discovered something that could be put in the bank!
That's really how you should look at it. Maybe try just one note from a new scale and give it a mere glimpse from an "inside" note.
This is where it's time to close the books and web browsers and just sit with the guitar, whack on a backing track loop and really listen to your note selection through each chord.
I can't tell you what's right and wrong. Only your ears can do that.
Some people might hear what Knopfler played and think it sounds "wrong". You and I are in agreement that it sounds beautiful.
But, at the end of the day, it's his interpretation that counts.