Though nascent in the eighteenth century, the rediscovery of fifteenth-century sacred music is really the achievement of the nineteenth. Enlightenment conviction in the eternal value of the works of men was a powerful force in late eighteenth-century efforts to uncover the vestiges of early musics. The idea of a viable aesthetic appreciation of fifteenth-century compositions emerged only later, in the work of the towering music historian of the midto late nineteenth century, August Wilhelm Ambros. The notion that Guillaume Du Fay was representative of a "School" is expressive of fundamental tenet of nineteenth-century music-historical formulations. This chapter attempts to explain why the music of the fifteenth century achieved the elevated status in the nineteenth. Driving forward the dialectical principle to the microcosmic level, Ambros focuses on imitation, the stylistic aspect of music beginning in the late fifteenth century that is probably most easily susceptible to a dialectical interpretation.