There are two divergent, almost opposing, schools of sacramental teaching, both of which have inherited the spirit of monophysitism. Both are instances of sacramental monism. First, there are those who identify the outward signs and the inward grace; second, those to whom the inward grace is everything and the outward sign nothing. Both schools of thought destroy the nature of a sacrament. The radical error of both consists in undervaluing the human and material. In the first case the error takes the form of the transubstantiation doctrine, which is exactly parallel to the extreme form of Eutychianism. According to Eutyches, the human nature of Christ was absorbed into the divine and lost there; the truth of His being was the divine personality; the human element was only an appearance. Similarly the transubstantiation theory conceives the mutation of the _substance_ of the material elements and the loss of their proper nature; the appearance of reality that the _accidents_ possess is an illusion of the senses. We may note in passing that the opposite error to transubstantiation finds its Christological parallel in Nestorianism. Socinianism which separates symbol from sacramental grace is sacramental dualism, as Nestorianism is Christological dualism. Both abandon a vital unity of divine and human. The pietistic or mystical view of the sacraments does so too, but in a different way. This second form of sacramental monism has much in common with the doctrine of one nature. To the pietist the divine seems all important, and the material no help, but rather a hindrance to the spiritual life. The faith of the individual to him is the seat of the efficacy of the sacraments; he regards matter as unreal if not sinful, and in either case unworthy to be a channel of divine grace. Echo after echo of monophysite thought can be caught here. The surest way to combat sacramental errors on both sides is a clear and definite statement of the catholic doctrine of Christology. NEED OF A MENTAL RECONSTRUCTION OF THE HUMAN NATURE OF CHRIST