The first thing that came to my mind today: Which is the fugue? The theme of the prelude, or the fugue proper? Today’s prelude sounds for all the world like a fugue, but the eighth note stepwise accompaniment is too stable to make this a proper counterpoint. Still, there is inversion of the theme, passing the theme between voices, and playing it in different keys. Perhaps JSB thought to himself, “yeah, close to a fugue but no cigar; let’s make it a prelude.” And the chromaticism — fasten your seatbelts. It appears to end the first section in the dominant, in order to render this early sonata form, but my ear isn’t sure that the midpoint really gets all the way to E. The fugue continues to mess with us — the subject stops after four notes, only to take off double speed with the same idea before it veers into what I call filler material — where does the subject end? One has to see how he “ends” the subject in other voices to form an opinion on what is subject and what isn’t. I think an “easy” key of A minor (no flats no sharps) encouraged JSB to pull our tails.