I did a live session a while ago and got lots of positive feedback about it! Lieven (Official Guide) took some notes about the lesson, so I thought I'd turn them into a full lesson, fill in the gaps and hopefully help you make sense of scales, why some notes get picked over others, and what effect they have. I will discuss the three main chord types, Major, Minor, and Dominant.

Major Chord

So to start here, I play a C Major chord into my looper; you might like to do the same. And then, I test each chromatic note over the chord and LISTEN. I'm going to tell you the effects now, but it's really important that you listen to them too, and the best way is for you to play them yourself, not just listen to me play them!

Triads
So the most stable and "safe" notes to play over the C Major chord are the notes that make up that chord, of course!! These would be the notes C, E, and G (1st, 3rd, and 5th notes of the C Major Scale), and they sound perfect with the chord, if perhaps a little boring.

7th
Adding in the 7th note of the scale (B) is pretty nice sounding, and this is the note that will make the chord Cmaj7 - if you were to play a b7 (Bb), it would then make the overall sounds a dominant chord! Play and listen, and you'll hear that it pulls to the root; it's not 'stable' and wants to resolve - meaning it created tension that needs to be released! The major 7th note adds some jazz flavor, whereas the b7 tends to sound kinda bluesy.

9th (2nd)
I love the 9th, the note D sounds real hip and super cool. It, too created tension that needs to resolve, but you can hang on to it a while, and if you use it right, it doesn't need to resolve... but if you do resolve it (take it to a stable note), it will go nice to either the C or E (a tone in either direction!).

11th (4th)
Now the 11th is the same note as the 4th (F), and it's a funny one... it creates a sus4 kinda sound and really wants to resolve to the 3rd, and you will probably let it!

13th (6th)
The last of our 'diatonic' notes is the note A which is the 13ths (or 6th). This also wants to resolve but is a very hip note to hang out on.

So far, we have now looked at all the notes in the C Major Scale but in a rough order of usability... although I think most times the 13th (6th) will sound better than the 11th (4th)...

Scale Degree	R	3rd	5th	7th	9th	11th	13th
Note	C	E	G	B	D	F	A

So now let's look at the less common notes and their effect on our C Chord...

b3
The minor 3rd over a major chord is troubled from the start, BUT it can sound great as a kind of blues note because the blues sound is built on playing minor scales (usually the minor pentatonic) over major chords. So you have to try it and see, sometimes it will be great, but the line is thin, and it might sound awful!!

#4 (#11)
This is the note that makes a "Lydian" sound (there is only one note difference between a Major Scale and The Lydian Mode, and it is the 4th (natural in the Major #4 in Lydian). It sounds hip over a Major chord but must be used with your ears on; it will either sound awesome or terrible!

b7
The flat 7, the note that makes a dominant 7th chord, will sound horrible over a maj7 chord but great over a 7 chord, so it must be used in the right place. That said, you could use it as part of a chromatic run, and it will most likely sound great!

#5
this note is unstable and will pull toward the 5th... sitting on it or resolving to it will probably not sound good!

b9
Because this note is just a semitone from the root note, it's probably going to sound dissonant and generally not nice, but you might get away with it if you play 9, b9, and resolve on the root, but you have to suck it and see.

Chart showing note qualities over a Major Chord

Scale degree	Note	Quality	Effect on tonality

1	C	CHORD TONE	STABLE
#1 / b2	C# / Db	very dissonant	Be careful!
2	D	interesting	Usually cool.
b3	D# / Eb	unstable	Sounds best going to 3 or root!
3	E	CHORD TONE	STABLE
4 / 11	F	needs resolution	Wants to go to 3
#4	F# / Gb	interesting	Listen and decide!!
5	G	CHORD TONE	STABLE
#5 / b6	G# / Ab	unstable	Be careful
6	A	interesting	Usually cool.
b7	A# / Bb	makes dominant 7 sound	depends on Maj7 vs 7
7	B	makes Maj 7 sound	depends on Maj7 vs 7

Over minor chords...

So what happens when played over a minor chord?? Well, give it some thought, decide what you think will happen, then read on...

In theory, the only difference will be the 3rd of the chord, which is a b3 for a minor chord. All the other notes will more or less be the same, BUT you have to listen to them because of the 'color' of the changes... they are still the same 'quality,' but they are somehow different.

The worst note is playing the major 3rd over a minor chord, it just sounds sour and yucky! Don't do it.

The Major 7th sounds pretty harsh on minor chords, too, try it and see.

The other main difference is that the 4th is much more stable than the minor... I find it strange how different notes can sound on different chord types.

The best thing is for you to be doing it yourself, either with a looper or a backing track.

Over other chords...

Well, what about playing over a G7#5b9 I hear you cry... well if you are at the point of playing over more complex harmony, I would strongly suggest that you explore this concept on your own, record a loop of the chord and play each chromatic note in the order and see what happens, listen, take notes, and then use what you learn!

I know this stuff is quite complicated, but understanding the value or quality of every note over a chord type will really help you get your head around scales and why they contain certain notes. It's fun once you get your head around it, and seeing scales as being 'chosen notes' should help you explore your lead line melody playing...

Get onto the forum if this stuff is doing your head in, and I'll try and improve it!