How did baroque composers write sequences that are both imitative and modulatory?

Question

Still working on my Bach-style fugue. And I wonder, how did composers of that time-period come up with all those sequential episodes in their fugues?

I know that there is a certain standard repertoire of sequences that readily lend themselves to imitation, such as the Monte Romanesca. Did Bach and his colleagues, if they wanted to use such sequences in a modulatory capacity, simply strategically slap accidentals onto them, or is there more to it? Also, most of those standard sequences feature imitation in only two upper parts. How common were modulatory sequences with imitation in three or even four parts, and how does one compose those?

Answer 1

It’s a great way to ensure formal coherence and, at the same time, variety.

How to do isn’t a cookbook recipe: you need to see your counterpoint, your harmonic progression, if you want reach a special key or chord, if you want to imply a new harmonic rhythm or sequence et cetera.

Try out some experiences, analyze some others masters solutions (Bach, Handel, Vivaldi, Buxtehude et al) and keep what you liked.