Impanation, an heretical doctrine according to which Christ is in the Eucharist through His human body substantially united with the substances of bread and wine, and thus is really present as God, made bread: Deus panis factus. As, in consequence of the Incarnation, the properties of the Divine Word can be ascribed to the man Christ, and the properties of the man Christ can be predicated of the Word (com municatio idiomatum), in the very same way, in consequence of the impanation—a word coined in imitation of incarnation—an interchange of predicates takes place between the Son of God and the substance of bread, though only through the mediation of the body of Christ. The doctrine of impanation agrees with the doctrine of consubstantiation, as it was taught by Luther, in these two essential points: it denies on the one hand the Transubstantiation of bread and wine into the Body and Blood of Christ, and on the other professes nevertheless the Real Presence of Christ in the Eucharist. Yet the doctrines differ essentially in so far as Luther asserted that the Body of Christ penetrated the unchanged substance of the bread but denied a hypostatic union. Orthodox Lutheranism expressed this so-called sacramental union between the Body of Christ and the substance of bread in the well-known formula: The Body of Christ is "in, with and under the bread"—in, cum et sub pane; really present, though only at the moment of its reception by the faithful—in usu, non extra usum. The theologians of the Reformed Churches, calling this doctrine, in their attack against the Lutherans, impanation, use the term not in the strict sense explained above, but in a wider meaning.
If we search for the historic origin of the term, we must go back to the controversies against the disciples of Berengarius of Tours at the end of the eleventh century. Guitmund of Aversa (d. before 1195), in his work "De corporis et sanguinis Christi veritate in Eucharistic" (P.L., CXLIX, 1427 sqq.), distinguishes two classes of disciples of Berengarius; those who absolutely deny the Real Presence of Christ in the Eucharist, and those who, though they admit that the Body and Blood of Christ are really (reverd) present in the Eucharist, reject the doctrine of Transubstantiation and explain Christ's Real Presence by a kind of impanation (Christum quodammodo impanari). Guitmund thinks this to be the essence of Berengarius's doctrine (hanc esse subtiliorem Berengarii sententiam). This teaching, however rightly or wrongly attributed to Berengarius, evidently does not profess impanation in the strict sense of the term; it rather coincides with the above-mentioned doctrine of consubstantiation as taught by Luther. Alger of Liege (1131), in his work, "De sacramento corporis et sanguinis Christi", I, 6 (P.L., CLXXX, 439-845), without mentioning any definite names, points out and opposes the errors of some (errantes quidam) who say that "Christ's Person is impanated in the bread, just as God is incarnated in the human flesh" (dicunt ita personaliter in pane impanatum Christum sicut in carne humanae personaliter incarnatum Deum). He calls this a heresy, which ought to be utterly rooted out, because it is an absurd novelty (quia nova et absurda). Who was it that introduced this new heresy? For a long time the well-known Abbot Rupert of Deutz (1135) was suspected. Cardinal Bellarmine (De Euch., III, xi, xv), Baronius (Ann. Eccl.: ad annum 1111, n. 49), Suarez, and Vasquez thought they could trace back the doctrine of impanation to him (cf. his work "De div. officiis", II, 2 and 9), and recently P. Rocholl ("Rupert v. Deutz", Giitersloh, 1886, 247 sqq.) repeated the same charge. Others, however, acquit him of this error, as Alexander Natalis, Tournely, and especially Gerberon in his "Apologia Ruperti Tuitiensis" (Paris, 1669); and, amongst modern writers of the history of dogmatic theology, J. Bach ("Dogmengeschichte des Mittelalters", I, Vienna, 1875, 412 sqq.) and Schwane ("Dogmengeschichte", III, Frei-burg, 1882, 641). They seem to be right, for a critical examination of all the passages bearing on the subject shows that Rupert, though at times he used ambiguous expressions, nevertheless believed in the Transubstantiation of the substance of bread into the Body of Christ. However this be, it cannot now be decided whether Alger of Liege cited Rupert as an advocate of impanation, since it remains unknown whether Rupert had already published his ambiguous expression at the time when Alger wrote his attack.
With much better reason, John of Paris (d. 1306) is considered the champion of the strict doctrine of impanation. In his work, "Determinatio de modo existendi corpus [sic] Christi in sacramento altaris alio quam sit ille quem tenet Ecclesia" (ed. Peter Alix, London, 1686), he tries, in conscious opposition to the Church, to establish, as plausible at least, the hypothesis that "the bread does not remain in its own sup positum, but is assumed through the Flesh or through the Body of Christ as a part of the esse and hypostasis of the Logos" (Ego dico panem ibi manere non in proprio supposito, sed tractum ad esse et suppositum Verbi, mediante carne aut corpore parte). Consequently, he maintains that it is correct to say: "The Body of Christ is `impanate', i.e. has become bread" (Corpus Christi impanatum, i.e. panis facturn); still it cannot be said that "the Man or Christ has become bread" (sed hominem aut Christum non possumus dicere impanatum), an explanation which is certainly not too conspicuous for clearness and precision. Amongst the reformers, Andreas Osiander (d. 1552), a fervent disciple of Luther, seems to have held the doctrine of impanation, though later Lutheran theologians have tried to acquit him of this error. It is, however, difficult to discern the real meaning of this fiery writer from his confused expressions. For this reason Melanchthon, in a letter of March 22, 1538, to the pastor Vitus Theodorus in Nuremberg, merely expresses his suspicion that Osiander held the doctrine of impanation. Both Melanchthon and Luther were thoroughly opposed to this absurd opinion. And this for many reasons, but especially because they would have been obliged to adore in the strictest sense of the word (cultu latrine) the bread hypostatically united with the Body of Christ, and this would have been in diametrical opposition to the Lutheran principles and practices of the Lord's Supper. Recently, Bayma, a Catholic theologian, in a series of theses proposed a theory on Transubstantiation, which, upon critical examination, comes very close to the above mentioned teaching of William of Paris; in fact, it 'seems to explain the Real Presence of Christ in the Eucharist by impanation. He bases his theory on the proposition that the substance of bread, in consequence of the conversion, ceases to be substance, and that it receives a new subject, without undergoing interior change, having its support no longer in itself but in another suppositum (substantia panis desinit esse substantia eo solum, et absque alia sui mutatione, quod in alio supernaturaliter sustentatur, ita ut jam non in se sit, sed in alio ut in primo subjecto). Consequently it is the Body of Christ that supports the nature of the bread (Corpus Christi sustentat naturam panis). Of this hypothesis, which denies a real Transubstantiation entirely, or admits it only nominally, the Holy Office justly declared: tolerari non posse (July 7, 1875-cf. Denzinger, "Enchiridion", 1843-46, 10th ed., Freiburg, 1908). The doctrine of impanation as far as it denies the Transubstantiation of bread and wine is certainly a heresy; besides, it is also against reason, since a hypostatic union between the Word of God Incarnate, or the God-man Christ, and the dead substances of bread and wine is inconceivable. Much less conceivable is such a union if we presuppose Transubstantiation, for since the substance of bread no longer exists it cannot enter into a by hypostatic union with Christ.