For a traditional approach to common-practice music theory, I’d very much recommend the lessons at https://www.musictheory.net/lessons https://www.musictheory.n

For a traditional approach to common-practice music theory, I’d very much recommend the lessons at https://www.musictheory.net/lessons https://www.musictheory.net/lessons It basically goes over what you’d expect to learn in the first few semesters of university-level music theory (though, that might’ve changed since my time…).