The Twenty-One Chapters of the First Book.

On the division and definition of music, Chapter I.
On the elements of musical practice, Chapter II.
What must be considered by beginners of this art in the diagram of Guido Referring to the "Guidonian Hand" or the hexachord system established by Guido of Arezzo, Chapter III.
On the clefs original: "clauibus," literally "keys" and the leading of voices through them; likewise, on the shapes of musical notes, Chapter IV.
On the five tetrachords tetrachord: a scale segment of four notes spanning a perfect fourth and the three types of modulation, Chapter V.
On the mutation of voices through all the clefs, Chapter VI.
On the transposition of signed or characteristic clefs, Chapter VII.
On musical intervals and how the species of intervals are to be determined, Chapter VIII.
What a pitch phthongus: the ancient Greek term for a distinct musical sound or tone is, as well as consonance and dissonance; also, how many species of consonances were recognized among the ancients and among the moderns, Chapter IX.
On the division of the whole tone and the definition of its parts, Chapter X.
A teaching on the eight musical modes modes: the system of scales used in medieval and Renaissance music of our age, Chapter XI.
On the endings of songs in the modes, Chapter XII.
On the common recognition of the modes, Chapter XIII.
On the range original: "expatiatione" and mixing of the modes, Chapter XIV.
On the use of the modes in a choir of singers, Chapter XV.
How musical consonances can be judged without doubt by the ear according to Boethius The Roman philosopher whose 6th-century work was the standard music theory textbook for a millennium, and therein concerning the misuse of musical terms, Chapter XVI.
What the bridge original: "magas", the monochord monochord: a scientific instrument with a single string used to measure musical intervals, the magadis, and similar names of certain musical instruments are, Chapter XVII.
On the threefold division of either the strings or the nerves The author uses "nerves" to reflect the ancient Greek word for gut strings in the musical scale, Chapter XVIII.
The division of the monochord in the diatonic genus, Chapter XIX.
On finding consonances by means of the strings of the lyre original: "cithara", Chapter XX.
A preparation original: "Paraſceue," a Greek term for a formal introduction or preparation for the commentary of the following book, Chapter XXI.

The Thirty-Nine Chapters

By what means the distinction of the modes is truly to be taken, Chapter I.
What a system is, what the names of the modes are, and which mode is to be fitted to each octave diapason: the Greek term for the interval of an octave, Chapter II.