I should also mention that my middle finger is the most double-tracked one and that he basically has two homes: Would be B and Bb on G string, F and F# on D string etc. Let's stay on D string. In case I go from G (ring finger) to F# (middle finger), from where I never slide (because I feel it doesn't sound right) it might go on with a slide to F, or the ring finger will end up there and finally slide home to E. But as baroque is not too chromatic, this won't happen often. I do like the slide from E to Eb on the D string though.

I know, I can basically shift my system and then play in F# major instead of F major, but my brain will emit ERROR--ERROR--ERROR. I would have to train that a lot, I had to conquer each key with hard work. Improvising works only if all fingers feel completely homey, you think about how you create melodic phrases and the fingers have to work right away.

By the way, today it just so happened that I added a famous song, written by a famous Lutheran Berliner pastor from the 1600s: "Nun ruhen alle Wälder" (Now rest all forrests). His name is Paul Gerhardt and I think I owe him that in December. Besides it's very beautiful. Well, I decided to sing it in Ab major, which would kill me on violin and recorder, so I change to Bb after the vocal part.