In two letters respectively dated May 6^th and June 12^th 1971, the Congregation for the Doctrine of Faith communicated to Professor Hans Küng the problems found in his books: The Church (1967) and Infallible? A question (1970) and requested that he should explain in writing in what way these statements were compatible with the faith of the Church. Professor Küng did not provide answers to this request. The same Congregation proposed, in a letter dated July 4^th 1973, that he should explain his ideas through dialogue, but professor Küng also refused this proposal in a letter dated September 4^th 1974.

At the time the Declaration Mysterium Ecclesiae, dated June 24^th 973, had already been published by the Congregation for the Doctrine of Faith but H. Küng had not provided any answers to the Congregation’s objections.

In that same Declaration he was advised that his statements concerning the doctrine of infallibility contradicted the position assumed by the First Vatican Council, a doctrine later accepted by the Second Vatican Council (see Lumen gentium, 25), because the statements reduced this infallibility to the Church’s indefectibility when confronted with errors, even reaching the point of stating that the Church remains within the truth in spite of her erroneous declarations. Furthermore Küng stated in his work that, when necessary, the faithful ‘s common priesthood could bestow upon them the power to consecrate the Holy Eucharist, thereby refusing to acknowledge that the priestly ministry as a sacrament is different to that of the faithful not only for degree, but also for its identity, and not only in view of ecclesiastic instructions, but rather in virtue of a dogmatic declaration, as written in the Dogmatic Constitution Lumen gentium (no. 10) published by the Second Vatican Council. Consequently both the German Episcopal Conference and the German and Italian ones appear to have pressed him to produce the more exact information that the Catholic faith requires.

At a later date – on February 15^th 1975 - the Congregation for the Doctrine of Faith was to publish a declaration in regard to Professor Küng’s publications, in which once again it indicated, in detail, the mistakes already observed: 1) the negation of infallibility, according to which the Church is certain that no mistakes are made on dogmatic issues in declarations pronounced by the Magistery. 2) The very function of the Magistery itself in interpreting authentically the revealed facts. 3) The comparison between the common priesthood of the baptised and the hierarchic ministerial priesthood as far as the celebration of the Eucharist concerned.

In spite of these positions contrary to the Church’s faith, hope always remained that H. Küng would rectify his mistaken positions. Pope Paul VI did in fact admonish him to teach in conformity with the doctrine of the Church and not in conformity with opinions contrary to this doctrine or even ones destroying the faith. The German Episcopal Conference, in a Communication dated February 17^th 1975 (adhered to also by the Swiss and Austrian Episcopates), contested that the Professor from Tubinga did not by assuming this position guarantee the permanent and compulsory characteristics of decisions taken by the Magistery of the Church, and therefore exhorted him to review his theological method.

In 1974 Professor Küng published his work entitled Being a Christian, in which he attacked the centrality of the Christian faith by presenting Jesus Christ simply as God’s substitute and not simultaneously as the eternal Son of the Father, consubstantial with the Father, who, after becoming a man, assumed the human condition as a single Person. This jeopardised the Trinitarian dogma of the unity and equality of the Persons, because, by denying the co-eternity of the Son one also denies at the same time the Father’s eternal generation. This also attacks the figure of Mary, denying her divine motherhood. According to Professor Küng in fact, she is a legend that appears marginally in the New Testament.

His book Does God exist? (1978) corroborated all he had previously stated; the author in fact approaches the realities of God, the Trinity and Jesus Christ, in a functional manner and not according to their ontic reality. To explain this with a Christological example, it is not sufficient to say that Jesus is God’s envoy in an incomparable manner, or even affirm His divine filiation, if this is not understood in its circumstantiality’s reality and its co-eternity with the Father, just as stated by the Nicene-Constantinople Symbol, a realty establishing a fraternal bond between the different Christian confessions.

The German Professional Conference returned to speak on these two publications on November 14^th 1977, indicting that these positions did not safeguard the integrity of faith in Jesus Christ and created problems in the ecumenical dialogue itself between the different confessions of faith.

In 1979 Küng returned to the subject of infallibility in two publications, a book entitled: Is the Church preserved within the Faith? And his Zum Geleit cooperation in A.B. Hasler’s work: In what way is the Pope infallible? The subject these two publications have in common is the statement according to which the infallibility of the Church inherent to definitive statements made by the Magistery does not exist and has never existed, it is also considered superfluous, and not proven in any way, neither in the past nor for the future, and also that the special assistance that the Holy Spirit provides to the Magistery cannot be proved.

According to Küng infallibility only exists in the sense of "believing" or indefectibility, thanks to which God’s People, through His grace, will always remain able to find the way of the truth, hence the right way for following Christ and remaining faithful to Him. This remaining within the truth however, is not to be found in the Magistery’s defining statements, because these are not infallible and for this reason will always be reformable. According to Küng, the First Vatican Council’s definition was a fraud perpetrated by Pius IX, which belongs within the framework of the Roman Curia but not within that of the universal Church; for him that word cannot be accepted by theology, hence he formulates the question: How could one define as "non catholic" those who agree with this?

Finally, faced with Professor Küng’s persistence in continuing to teach while professing to do so in the name of the Church, the Congregation itself and the Bishops involved in this matter attempted to put an end to these claims, but faced with the persisting situation, could not prevent the faithful from becoming confused by positions contrary to the faith. For this reason the Declaration concerning a number of points contained in the theological doctrine of Professor Hans Küng was emanated on December 15^th 1979, in which it was declared that this doctrine not only questioned but explicitly denied the Roman pontiff’s infallibility in matters of faith and precepts, proclaimed a dogma by the First Vatican Council (See Pastor aeternus, chapter IV: DS 3074). Furthermore, Küng has falsified the sense in which the Catholic Church has understood the affirmations of faith in the divinity of Jesus Christ and consequently in the divine motherhood of Mary, due to the fact that dogmas constitute an organic unit and, if the integrity of one is attacked then so is the totality of the system. However there is no intention of denying that a hierarchy of dogmas exists, but neither does it mean that the teachings of the faith can accept partial acceptance for some definitions, while for others believers’ acceptance is optional.

Consequently, when the Congregation for the Doctrine of Faith was presided by Cardinal Franjo Seper, with the approval of His Holiness Pope John Paul II, it approved that the Congregation itself should declare Hans Küng a non Catholic theologian for having failed the integrity of the Teachings of the truth of the Catholic faith, hence he no right to teach in the name of the faith.