How did music differ before and after bach?

The introduction of Bach to music had quite an impact. Before Bach, many were ill - tempered and most became well - tempered after Bach. Harmonically speaking, Back's composition were way ahead of time. He introduced unexpected chord changes. He also initiated the keyboard  technique that is still used up to date. 

The answer is true back then the word conversation had a different meaning then what we use it for today

What does that mean