The purpose of the study is the investigation of the topics of transposition and the transposed major and minor modes as discussed principally by selected French authors of the final twenty years of the seventeenth century and the first three decades of the eighteenth. The sources are relatively varied and include manuals for singers and instrumentalists, dictionaries, independent essays, and tracts which were published in scholarly journals; special emphasis is placed on the observation and attempted explanation of both irregular signatures and the signatures of the minor modes. The paper concerns the following areas: definitions and related concepts, methods for singers and Instrumentalists, and signatures for the tones which were identified by the authors. The topics are interdependent, for the signatures both effected transposition and indicated written-out transpositions. The late Baroque was characterized by much diversity with regard to definitions of the natural and transposed modes. At the close of the seventeenth century, two concurrent and yet diverse notions were in evidence: the most widespread associated "natural" with inclusion within the gamme; that is, the criterion for naturalness was total diatonic pitch content, as specified by the signature. When the scale was reduced from two columns to a single one, its total pitch content was diminished, and consequently the number of the natural modes found within the gamme was reduced. An apparently less popular view narrowed the focus of "natural tone" to a single diatonic pitch, the final of the tone or mode. A number of factors contributed to the disappearance of the long-held distinction between natural and transposed tones: the linking of the notion of "transposed" with the temperament, the establishment of two types of signatures for the minor tones (for tones with sharps and flats, respectively), the transition from a two-column scale to a single-column one, and the recognition of a unified system of major and minor keys.