 More troublesome in the eyes of the Church was John's treatise on the Blessed Sacrament, in which he maintains that the Body of Christ is, or might be, present by assumption (i.e.by the body of Christ assuming the bread and wine), and that the doctrine of transubstantiation is not of faith.It must be said, however, that he advances these propositions tentatively; in the beginning of the treatise he writes that he believes in the Catholic doctrine of transubstantiation and that if it is shown that transubstantiation is of faith, or should it be so defined, he will willingly retract.