This book provides an in-depth study of the late medieval chanson, from Gace Brulé through Guillaume Du Fay. It is largely concerned with interpretation of the way accidentals function, not only at the level of local detail but also as part of the overall design, and explores the way inflections are used by the composer as an expressive tool. Support for this approach comes from reference to causa pulchritudinis ("by reason of beauty"), a justification for chromatic writing first encountered at the beginning of the fourteenth century.