When I'm teaching improvisation, one of the most commonly asked questions is “Which scales work over what chords?” I frequently answer this question by pointing out that it depends entirely on what you consider the 'working' to mean?
What is a scale ‘working’ over a chord anyway?
Where this may appear not to answer the question at all and be a thoroughly unhelpful digression into the philosophical implications of perception, it’s actually worth thinking about because the whole idea that certain ‘prescribed’ scales work over certain chords, chord types, or chord sequences is actually rendering music and improvisation a sterile by-product of a prescribed approach, and a institutionalised ‘system’.
Using jazz as an example, there are some people who hate this style of music for whom the whole idea of a scale “working” over a chord or chord sequence (as a player improvises) is as far removed from a good idea as can be! Some may consider a scale ‘working’ over a chord progression to be dull, boring, and most probably the least inspirational music they may be exposed to. While rightfully entitled to their opinion, to what extent is this scale ‘working’ for them? It isn’t, so does the scale ‘work’ with the chord or chord sequence? It depends who is listening, and in the space between the extremes in musical taste (someone who hates jazz, and a jazz lover) the question of whether or not, and if so the extent to which a scale may ‘work’ over a chord, has many, many manifestations of answer, none right nor wrong, none more or less accurate than the previous or last, and the reason the question “Which scales work over what chords?” is ultimately vague, subjective, and with no real definitive answer.
Clearly it’s a good thing to learn which scales work over certain chords in a conventional sense. This starting point is invaluable for the serious and committed student of improvisation, but as I frequently say to my students, the scales, modes, and arpeggios which are most commonly ‘prescribed’ to work over certain chords and sequences don’t actually serve to help you to sound good. They serve to help you avoid sounding bad (which is not the same thing). Who wants to sound good anyway? Doesn’t the aspiring guitarist want to sound ‘great’? Don’t they want to play with their own voice, unrestricted by any technical or musical constraints that may stand in the way of them truly expressing what they really mean? The idea that someone wants to sound ‘good’ seems like one step too close to mediocrity when compared with the actual level that a player may aspire to!
Still want to know which scales work over which chords? You can find all that information on the internet.
Wouldn’t you rather know how to be a great guitarist? To find that out, the only way is to think about what scales ‘working’ over chords means to you, and then asking some better, and more personal questions about it regarding how you really want to sound.