Maybe some musicologists dispute the authorship of that work, but who else could have wrote it? Just compare that youthful composition to the 7 toccatas for harpsichord BWV 910 à 916, and the stylistic link will become obvious.
There is the belief that this piece began its life as a work for unaccompanied 5 string cello (or even violin): the fugue subject lies very well for that instrument, and Bach is known to have transcribed at least one of his solo violin pieces for organ. See this article .
The earliest known manuscript copy for organ is in Berlin, Staatsbibliothek Preussischer Kulturbesitz, Musikabteilung.
Generoso 16:13, 21 January 2012 (UTC)