De preceptis is considered a major source of information on the origins of fauxbourdon, despite its being regarded as a disorganized compilation of multiple authorship, uncertain date, and unknown provenance. Internal cross-reference and writing mannerisms, however, show it to be a compilation of a single author's writings. Comparison of its pedagogical content to that of other theory treatises suggests that it was written c. 1500, not the accepted c. 1480. Evidence also indicates that Guillaume Garnier, a Flemish associate of Tinctoris and Gaffurius working in Italy, was its author. De preceptis ought to be considered a source, not for the origins of fauxbourdon, but for its reception-history, evidenced by the centrality of the parallel-consonance duet in Guilielmus's composition formulas, many of which resemble the frottola.