In his treatise on harmony Fetis studied this evolution in a masterly manner.

Unfortunately his scholarship was not combined with deep musical feeling.

For example, he saw faults in Mozart and Beethoven where there are only beauties, and beauties which even an ignorant listener--if he is naturally musical--will see without trouble.

He did not understand the vast difference between the unlettered person who commits a solecism and Pascal, the inventor of a new syntax.
However that may be, Fetis gave us a comprehensive review in broad outlines of musical evolution down to what he justly called the "omnitonic system," which Richard Wagner has achieved since.

"Beyond that," he said, "I can see nothing more." He did not foresee the a-tonic system, but that is what we have come to.
There is no longer any question of adding to the old rules new principles which are the natural expression of time and experience, but simply of casting aside all rules and every restraint.
"Everyone ought to make his own rules.