Originally posted by Aragorn
Well, to use a worn and also not scientifically correct metaphor, it's a left-brain/right-brain thing. On the one hand, most people have enough of a musical intuition to develop at least some sense of melody and rhythm. On the other hand, knowing at least the basics regarding the theory can assist the intuitive aspect and lead to a greater understanding of what you're doing, which in turn leads to greater creativity.
The reason why pentatonic scales grew to popularity so quickly and as such became the foundation of the blues — a musical genre that developed among the African-American slaves — is that they are purely intuitive and that they thus don't require any musical understanding at the intellectual level. And that's where the problem lies for Lee. Due to the widespread adoption of the blues in modern western music, he had always been approaching things from the purely intuitive vantage and sticking to those pentatonics without concerning himself too much with the theoretical aspects of music.
However, studying the theory without being able to relate this knowledge to the playing of the instrument of your choice is no good either. You have to be able to match the two together in order to be a creative musician. And eventually, it then becomes second nature. At least, if you really want to be a good musician.
But due to the complexity of music as a whole — especially when dealing with chromatic scales, as in jazz — most musicians, even good ones, know only a subset of the complete music theory and mostly rely on their intuition. Almost every human being has an intuition for music. Those who do not — and such people do exist — are people with a certain genetic condition, because even animals intuitively understand the concepts of rhythm, frequency and harmony. And as such, if we discount those people with a genetic predisposition for not having any musicality at all, most people are capable of learning how to play a musical instrument.
Of course, mastering the instrument itself is yet again another matter. A guitar normally has six string courses — let's for a moment discount the different varieties with another number of strings and/or string courses, such as the tenor guitar, which has only four strings and is tuned to different intervals — and they are tuned in intervals of fourths, except for (from high to low) the second and third strings, which have an interval of a major third.
Every fret on a guitar also represents a semitone step. As such, there is no distinction between the diatonic and chromatic notes, unlike on a piano, where the white keys always represent the diatonic notes belonging to the key of C Major, while the black keys represent the notes that are considered blue notes in C Major, and the black keys are positioned a little higher than the white keys, and they are also shorter. And then there are the flutes, the woodwinds and the brass wind instruments, which are monophonic instruments — they can produce only one tone at the time, whereas guitars and pianos are polyphonic. All of these instruments require a different technique for producing the notes you want to play, and mastering one instrument does not imply in any way that one would then also be able to play any other instrument without practice.
But returning to the subject of the left-brain/right-brain dichotomy, here's an extreme example of either one... The late B.B. King was considered a blues virtuoso, and was known for his clever variations and creativity. And yet he couldn't play any chords on his guitar, nor could he read sheet music — which in itself is not a requirement at all, because even someone as experienced and knowledgeable about music theory as Steve Lukather cannot read sheet music.
And at the other end of the spectrum, there is my brother's ex-wife, who used to play a flugelhorn in a brass band. She had attended music school, she could read the notes, and she knew how to produce those notes on her instrument, but she had no sense of melody, and there wasn't even as little as a shred of musical creativity within her. She could not just play a tune — any tune, for instance from a popular song — at will, and she cannot relate to either the melodies or the harmonies. She also has no sense of pitch when she tries singing along with a song on the radio. She goes flat and sharp all over the place. On the other hand, she does however have at least some sense of rhythm, or else she wouldn't have been able to play along in the brass band.