Thus it was that already in the first four or five centuries of Christianity almost all the errors possible against the Incarnation were proposed.

1) The divinity of Christ was denied. In the first century, by the Ebionites and Cerinthians. In the second and third centuries by the Adoptionists and Gnostics.

In the fourth century, by the Arians. They declared that Christ is not the Son of God consubstantial with the Father but is a creature; that the Word (Logos) pre-existed, but was created, and is a mediator, who assumed in the womb of the Blessed Virgin Mary only a body and not a soul. Thus the Arians concluded that Christ is neither truly God nor truly man. Hence St. Athanasius replied[384] that such a conception of Christ made it impossible for Him to satisfy for the human race or free it from sin. This means that the denial of the mystery of the Incarnation includes the denial of the mystery of Redemption, and thus there is left but the semblance of Christianity.[385]

Later on, in the sixteenth century, the Socinians denied the divinity of Christ, and the same must be said in our times of the Unitarians, who deny the Trinity, and also liberal Protestants and Modernists of the present day.

2) The humanity of Christ. Some denied that Christ's body was real, others that He had a soul. The Docetae, such as Marcion and the Manichaeans, said that Christ merely appeared to have a body.

Appelles and Valentinus in the third century said that Christ's body was real but celestial, sidereal or aerial, and therefore He did not derive His human nature from the Virgin Mary.

The Arians and Anomoeans taught that the Word did not assume a soul. In the fourth century the Apollinarians held that Christ had only a sensitive soul, and that the Word performed the functions of the rational soul, though they admitted, contrary to the Arians, that the Word was not created.[386]

3) Some denied the unity of person in Christ, others the twofold nature. In the third century, the unity of person was denied by Paul of Samosata. In the fourth century, Diodorus of Tarsus said that the Word was only accidentally united to Christ. So also Theodore of Mopsuestia and the Nestorians, teaching a sort of personal union, rejected it really, however, inasmuch as they posited merely a moral union between the two natures. In this way they sought to refute Apollinarianism. The consequence of these errors was the view that Mary is not the Mother of God.

The prominent opponent of the Nestorians was St. Cyril of Alexandria who, in refuting them, availed himself of the principal argument used by St. Athanasius against the Arians, namely, that, if Christ is not God, but only morally united to Him, as a saint is, then how could He satisfy for us or free the human race from sin?[387]

In our times, too, the disciples of Gunther denied the unity of person in Christ, since they defined a person as a self-conscious nature, for in Christ there are two self-conscious natures.

So also, Rosmini acknowledges between the Word and the human will in Christ merely an accidental union, inasmuch as the human will, since it was completely dominated by the Word, ceased to be personal. Rosmini says: "Hence the human will ceased to be personal in Christ as man, and, since it is personal in other men, in Christ there remained but the human nature."[388] Thus the union in Christ between the Word and the human will would be merely accidental and moral. The error of Rosmini and Gunther is that both do not seek to define person ontologically by reason of subsistence, but only psychologically through self-consciousness, or by reason of liberty. This error is the result of the nineteenth-century psychologism.

The Modernists say about the same, since they reduce the hypostatic union, if they give it any thought, to God's influence upon the human conscience of the historic Christ, or to the subconscious self in Christ by which He perceived that He was loved by God above all others.

Finally, the Eutychians or Monophysites denied that there were two natures in Christ. Eutyches posed as the adversary of Nestorius and the defender of the theology of St. Cyril of Alexandria, which he did not understand. He was a man of little learning, and obstinate, and so he went to the other extreme of Nestorianism. He was so insistent in affirming the unity of person in Christ against the Nestorians that he ended in denying His twofold nature. He said: "I confess that our Lord was of two natures before the union; but after the union I acknowledge one nature,"[389] either because the human nature was absorbed by the divine nature, or because each nature commingled to form a third nature, distinct from each before the union, or because the human nature and the Word were absolutely united as the soul and the body are. Hence Eutyches by this method succeeded in proclaiming something that the Nestorians denied, since they denied that the Blessed Virgin Mary is the Mother of God.

In the fourth century, however, the Monothelites, professing that Christ had but one will, by this very fact rejected the doctrine that there were two natures in Him. The followers of the modern heresy that declares the Word really emptied Himself, also deny a twofold nature in Christ, since they hold that the Word, at least partly and for a time, set aside His divine attributes.[390]

Thus several heresies made their appearance as excessive reactions against the preceding ones; so also not infrequently it happens that the human mind in its aberrations passes from one extreme to the other.