As to the debate about the unicity of substantial form, Giles’ position evolves during time. If we leave aside the Errores philosophorum, since the authenticity of this work has been contested with serious arguments (Bruni 1935, Koch 1944, Donati 1990b, Luna 1990), we can notice that Giles changes his position from the Contra gradus et pluralitatem formarum (between the end of 1277 and the beginning of 1278), where he, against Henry of Ghent denies plurality of forms for every compound (Wilson 2