The definitive work titled Tonal Harmony in Concept and Practice
Tonal harmony in concept and practice : Forte, Allen : Free Download, Borrow, and Streaming : Internet Archive. Internet Archive
Some professors have legally created annotated PDFs for their students, updating examples with jazz/pop parallels. These are often shared via course management systems like Canvas or Moodle. If you are self-studying, consider auditing a free online course (e.g., from Berklee or Coursera) that uses Forte’s text.
A stronger focus on applying harmony at the piano, which is essential for internalizing the sound. Practical Application: How to Study Harmony