The title "Fantasie 'duobus subiectis'" (Fantasy on Two Subjects) is found in a manuscript by Johann Christoph Bach. Here, "Fantasie" refers to a contrapuntal work. Although titled "on two subjects," there are actually three: a descending fourth including chromaticism (in the alto at the beginning), a melody with leaps and suspensions (in the bass at the beginning), and a counter-subject consisting of a series of eighth notes with turns (in the soprano at the beginning). The "second" subject indicated by the Latin title might refer to this counter-subject. In any case, this method of combining subjects with distinct characteristics is a hallmark of Bach's contrapuntal compositions.

While maintaining strict four-part writing throughout, the texture is clear and does not lose its elegance. Given its brevity and Latin title, it might be considered a contrapuntal study or pedagogical piece, but one should not judge this work solely by its scale or format. It is a fine work, utilizing only carefully selected and maximally refined notes.