While scholars have questioned the authenticity of this little fantasy, this composition exists in a Bach family manuscript, with Bach clearly named as the composer. What's stranger about the piece is its title: "Fantasie duobus subiectis." It promises two subjects, but there are actually three, and that doesn't count the miniscule single-voice toccata that begins the fantasy. The work's main matter is a sober, moderate-to slow-tempo imitative fantasy in which the three voices polyphonically intertwine. This is not a full-fledged fugue, but merely a skillful exercise in counterpoint, different from Bach's famous Three-Part Inventions (Sinfonia) only in its grave nature and the presence of the little opening toccata.

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