The descriptions of the Basilidian system given by our chief informants, Irenaeus (Adversus Haereses) and Hippolytus (Philosophumena), are so strongly divergent that they seem to many quite irreconcilable. According to Hippolytus, Basilides was apparently a pantheistic evolutionist; and according to Irenaeus, a dualist and an emanationist. Historians such as Philip Shaff have the opinion that "Irenaeus described a form of Basilidianism which was not the original, but a later corruption of the system.