I have often likened improvised lines to little trips away from home, with "home" being the I - III - V of the "chord of the moment". These are usually, and I stress 'usually', your starting notes and finishing notes. The other notes used to link home notes can be any of the twelve notes of the chromatic scale. Naturally, the II, IV, VI, and VII (which are the other scale notes) will be favorites, but any of the others (non-scale notes) can be seen as linking notes - notes not to linger on, but notes to fill the gaps. Basically, any fret will do. However, timing becomes paramount. "Phrasing" might be a better word. You must mold your line so that you wind up passing through the home notes at the right time, and most importantly, resolving them on time. By that, I mean get home on time. How do you do that?

Another way of looking at it: you create a simple melodic line, one that fits the changes, and then you fill in a few gaps (in space and time) with notes from the chromatic scale. Before long, you know what every one of those twelve notes sounds like in context. You'll know where each one leads, and which tensions are set up and resolved with which notes.

A good example is the blues. Again, I never think "blues scale", but I know that (in a major key) the III hovers between the minor and major versions. It never settles, so I avoid it as a resolve note. I know that the seven is the dominant 7th, the flat VII. So I make sure it winds up in my lines, not the major seven. The flat VII really is a blue note, and can be used as another home note. All intervals can be linked with semitones. Strictly major music never uses the flat three and only uses the flat VII for the V chord.

Major key music which isn't the blues never uses the flat III and uses the major seven, except for the V chord, which uses the flat seventh. (Why? Because it's one of the scale notes.)

Minor music is minor music. I was asked that question in another letter.

What is a minor key?

Ill answer that next time.