Of Universal Harmony

XXI. To explain the manner of singing all sorts of Duos in simple counterpoint A style of composition where each note in one voice is matched by a single note of equal duration in another voice., or note-against-note, and the rules that must be observed in this kind of Composition. 256. Wherein 3 or 4 fundamental rules of Composition are seen. 256.
XXII. To provide the method for composing Duos in note-against-note style: where the true understanding of the rules of Composition is found. 262.
XXIII. To consider three other Duos, and everything necessary to compose as many of them as one wishes. 264.
XXIV. To show that one can use certain Dissonances in Duos of simple counterpoint, and the method of composing Trios Compositions for three voices or instruments. in note-against-note style. 267.
XXV. To provide the theoretical concept for the examination of the preceding Trios. 269.
XXVI. To explain the other parts of Composition and their properties, and how one must compose for four parts. 272.
XXVII. To explain the method of composing for five parts in note-against-note style, and consequently for three and four parts. 276.
XXVIII. To examine two compositions for six parts, written by Eustache du Caurroy A prominent French composer of the late Renaissance (1549–1609), known for his complex polyphony.. 279.

I. To explain what belongs to figured counterpoint Also called florid counterpoint, this involves more complex rhythms and decorative melodies compared to the "note-against-note" style., and to provide examples of the twelve Modes The system of scales used in music before the modern major/minor system became standard.. 283.
II. To explain the practice of Dissonances. Wherein are seen particularly the examples of the second and the ninth. Now, the Printers having consistently failed since page 191 (which they put in place of 291) up to page 323 (which begins to be correct), I shall mark the propositions according to what the numbers ought to be, and not following their error.
III. To explain a certain kind of harmonic syncope A rhythmic technique where a note is held across the beat, often creating a suspension or temporary clash with other voices., which practitioners do not call a syncope. 294. But the Corollary of the 5th proposition provides examples of true syncopes.
IV. To explain the use of the Tritone An interval of three whole steps, historically called "the devil in music" for its harsh sound., the Semidiapente A diminished fifth, an interval slightly smaller than a perfect fifth., and the Seventh in Duos. 195. original: "195." This is one of the printer errors Mersenne refers to above; it should likely be page 295.
V. To provide examples of all Dissonances in compositions for 3 and 4 voices, and all possible ways of employing the Fourth. 298.
VI. To explain the practice of Consonances, and the sequence they can maintain between themselves to create agreeable Compositions. 307.
VII. To explain false relations A melodic or harmonic clash that occurs when a note and its altered version (like F and F-sharp) appear in different voices in close succession., the use of which practitioners condemn. 312.
VIII. To explain the Cadences The sequence of chords or notes that brings a musical phrase or piece to a rest or conclusion., whether perfect, imperfect, or broken, which are used in Music. 315.
IX. To explain Fugues A composition where a short melody is introduced by one part and then taken up by others in succession. and counter-fugues, along with Guides, Consequences, Imitations, and Canons. 317.
X. To determine what must be observed to compose excellently for 3 and 4 parts. 321.
XI. To explain the manner of regulating and beating the measure The marking of time or rhythm. of Music in all sorts of ways. 324. See the 18th proposition of the 3rd book on Instruments.
XII. To explain everything belonging to the Modes and tones of the Greeks and of the