Once again, I have been confronted with the wild and bold choices of JSB. This time, it’s from BWV 172. I was accompanying this yesterday and was shocked to see that fourth measure. (You can expand the picture by clicking on it.)
That’s right. Over a pedal G, the choral parts expand the V7 by going to a IV(7 9)??? and then back to the dominant. I would never allow a student in harmony class to write this.