Prelude in em - well tempered clavier vol 2 - js Bach

Prelude in em - well tempered clavier vol 2 - js Bach

So what is it that makes a prelude? Is there a strict form structure that it must follow?

In this piece, I noticed that there are only two voices and they often play off the melody (though the right hand gets more of the melody). Oftentimes the right hand plays a long melodic phrase which is then taken up only in part by the left before it gets stolen back and modified into something new by the right hand. Because of the two voices, and their often homophonic qualities, the cadences are much clearer than in the fugues. Oftentimes, it seems as though the piece will end, but then continues. There are a lot of mounting motives/sequences and a lot of trills thrown back between the two voices. There's a big cadence in the middle of the prelude where it tries to hang out in major afterwards for a while, but then keeps playing around and falls back into minor. Then cadences again as though it will end, and is interrupted by a trill in the right hand and again flirts a little bit with major, cadencing in minor, moving back to major, then minor, a long trill in the left hand who's voice becomes more apparent. It tries to cadence, then goes for one last go in minor and then ends for good.

-of course I chose the minor, and I listened to it on harpsichord, because I just don't feel piano does it justice. There's something in the timbre that brings back so many associations.