From Zappa Wiki Jawaka
Walter Piston (January 20, 1894 - November 12, 1976) was an American composer, music theorist and professor of music at Harvard University. Some of his students included Leroy Anderson, Leonard Bernstein and Elliott Carter.
Piston wrote four standard books on music theory. Zappa read his "Principles of Harmonic Analysis" while he was at high school.
"The standard theory that I know is really quite limited because I always found it quite boring. I got a hold of the Walter Piston harmony book when I was in high school and I went through some of the exercises in there. And I was wondering why a person would really want to devote a lifetime to doing this, because after you complete it you'll sound like everybody else who used the same rules. So I learned enough of the basic stuff so I got the concept of what harmony was supposed to do, what voice leading was supposed to do, how melody was supposed to function in a harmonic climate, what rhythm was supposed to do. I learned all of that and then chucked the rest of it." (Frank Zappa, quoted from Frank Zappa: The SongTalk Interview)
Interviewer: "When Charles Ives was at Harvard studying harmony he was going crazy the way you're describing, and he wrote home to his father, saying, "This guy wants me to resolve my chords better," and his father wrote him back and said, "Tell your professor some chords just don't want to resolve."
Frank Zappa: "Well, you can tell it to a professor if you have that kind of a relationship with a professor. I mean, I really didn't have professors. The harmony training I got was because I was an unruly senior in high school, and they gave me permission to take some harmony classes at the adjoining junior college. They figured that the reason why I was such a delinquent was because my mind wasn't occupied. So they let me take this course at the junior college while I was senior. The guy who was teaching it was a guy named Mr. Russell, who was a jazz trumpet player, and I don't think that he enjoyed harmony very much either, but that's what he was teaching. I could have said to him, "Hey, some chords shouldn't resolve." And he would probably say, "Yeah, but you'll get a D if you don't resolve them."
Interviewer: "What book did he give you? Was it Walter Piston's Harmony?"
Frank Zappa: "Yeah, it was Piston."
Interviewer: "That's a hard one to stay awake through."
Frank Zappa: "You remember? I hate to read also. It's very difficult for me to digest any kind of information in that way. I'm pretty good at the news magazines. But even with all the digital equipment that I've got, I've almost never cracked a manual on any of it. Basically, I've learned how to work it by just having somebody show me. And then after I've learned the basics, I'll figure out ways to make the system do stuff that was never in the book in the first place."
(Quoted from The Mother of All Interviews (Part 1))