I am a composer and teacher of music theory - and have been for many years, both in an institutional and private basis. I have been using the Piston Harmony books for nearly thirty years, starting with the 3rd edition, onto the fourth, and then the fifth.When I got into the fifth edition I found that much of the clarity was destroyed and much superfluous material was added. The third was too terse, with not enough helpful explanation. The fourth edition is by far the best harmony book I have ever seen,and although I have not seen all of them, I find no reason to change from a perfectly clear system to anything else.[...]