In the 2008 book "Catholicism and Science", the authors Peter M. J. Hess and Paul Allen wrote that "sola scriptura" is "inherently divisive", citing the Marburg Colloquy where Martin Luther and Huldrych Zwingli debated the real presence of Christ in the Eucharist on scriptural grounds but were unable to reach agreement on Sacramental Union. Hess and Allen argue that, when scripture is seen as the only source of infallible teaching, its interpretation is subject to fallible interpretation, and without an infallible interpreter, a certainty of Christian belief is not possible.