's mastery of triple counterpoint is evident in all of his works based on the compositional technique. These pieces include the Sinfonia (Three-Part Invention) in D major, BWV 789; the Prelude in A major from The Well-Tempered Clavier, Book I, BWV 864; the Fugue in F # major from The Well-Tempered Clavier, Book II, BWV 882; and the Sinfonia in F minor, BWV 795. Of these, the Sinfonia in F minor stands out, by virtue of Bach's bold departures from conventional practices of dissonance treatment and harmonic syntax with respect to six-four chords, licence that he takes to accommodate thematic material in the bass.This essay explores several interrelated musical components central to the extraordinary nature of the piece: the polyphonic structure of the subject and the transferred resolution of its most prominent dissonance; the above-mentioned departures from conventional treatment of six-four chords; the altered linear and harmonic meanings of the three lines -subject (S), countersubject (CS1) and second countersubject (CS2) -in the context of modulation via auxiliary cadence; Bach's use of particular permutations to mark with perfect authentic cadences both keys and sections of form; and his use of certain permutations to create a prolongational structure on a deep middleground level.A formal chart of the piece (Table 1) indicates bars, permutations (or vertical arrangements of the subject and countersubjects), thematic statements and episodes, keys, cadence types and several other factors discussed in the course of the essay. I follow Daniel Harrison (1988) in treating the 'conjugation' as an important formal indicator and source of compositional technique in the context of triple counterpoint (Table 2): there are six possible arrangements of the three lines in triple counterpoint; the two conjugations are the two collections of three arrangements each in which each line appears once in each voice.1 The essay also briefly explores the views of the eighteenth-century theorists Johann Philipp Kirnberger and Friedrich Wilhelm Marpurg regarding six-four chords in invertible counterpoint; Bach's employment of melodic and cadential formulas common in eighteenth-century fugue and partimento; and the descriptions of those cadential formulas by several seventeenth-and eighteenthcentury theorists.Throughout much of the essay I employ conventional Schenkerian analytical techniques, including some methods particularly applicable to the study of imitative counterpoint, such as the examination of the polyphonic and harmonic content intrinsic to many fugal subjects and the reduction of the melodic Music Analysis, 34/iii (2015) 305