Two books I'll throw in here: Foundations of Diatonic Theory [0] which gives the simplest, modern, math-based explanations of how notes and chords relate. It's

Two books I'll throw in here: Foundations of Diatonic Theory [0] which gives the simplest, modern, math-based explanations of how notes and chords relate. It's a college workbook that you write-in for the exercises. Really terrific. Also, not a theory book but the most important music learning book I've read: The Perfect Wrong Note [1]. Reading this permanently changed the way I approach learning the piano (or synth. in my case) and I my playing has vastly improved over the last couple of years because of it. [0] https://rowman.com/ISBN/9780810862333/Foundations-of-Diatonic-Theory-A-Mathematically-Based-Approach-to-Music-Fundamentals https://rowman.com/ISBN/9780810862333/Foundations-of-Diatoni... [1] https://www.halleonard.com/product/331733/the-perfect-wrong-note https://www.halleonard.com/product/331733/the-perfect-wrong-...