oa Henricus Isaac’s Lost Missa Je ne fay plus Found?

In a 1532 letter to Pietro Aron, Giovanni Spataro cites an unusual ligature in the Tenor of the Patrem in Isaac’s Missa de Je ne fays’. The mass, probably based on Gilles Mureau’s famous chanson Je ne fays plus, has up to now been considered lost. This study identifies Mureau’s chanson as the model of an anonymous Missa Sine nomine in the Kodex Leopold (Munich, Bayerische Staatsbibliothek, Mus. ms. 3154), and demonstrates that this is mass is identical to that described by Spataro: although the manuscript abandons the unusual ligature, it preserves its rhythm and melody, resulting in errors consistent with Spataro’s identification. Shared stylistics with Isaac’s Missae Argentum et aurum and Et trop penser and his motet Salve regina strongly favour Isaac’s authorship of the mass. The article also considers stylistic features that align the mass with works of Isaac’s thought to be early, as well as with pieces by his German contemporaries Fulda and Finck, and with Obrecht. All features taken together argue for adding this Missa Je ne fay plus to Isaac’s canon with confidence and suggest that it belongs to an early period of his career. This conclusion raises the question of whether it is possible to differentiate between career-long stylistic traits and those from different periods in Isaac’s works.