[Code of Canon Law]
"No doctrine is understood as defined infallibly unless this is manifestly evident."
--749 Section 3
[Vatican Council I]
The object of infallibility in the Church, and consequently in the Roman Pontiff, extends to all those things and only to those things which either directly pertain to the revealed deposit itself, or are required in order that the same deposit may be religiously safeguarded and faithfully expounded. And this is the infallibility which the Roman Pontiff, the head of the college of bishops, enjoys in virtue of his office, when, as the supreme shepherd and teacher of all the faithful, who confirms his brethren in their faith, he proclaims by a definitive act a doctrine to be held concerning faith or morals. But let this be noted well: there is a huge difference between definitions of dogmas on the one hand and the reasons which are brought forward and added by the Pope in order that these definitions may be understood. Therefore, in those things which are determined by definitions, the assistance of the Holy Spirit promised to the successor of Peter is present; in other things, however, which are added to the definition, either to prove it or to explain it or to make it clear, the Pope is not protected by the charism of infallibility. Hence, we do not define the reasons [arguments or subordinate clauses] which the Pope brings forward, but rather the definition itself.
--Bishop Vincent Gasser, The Official Relatio on Infallibility at Vatican Council I (July 11, 1870), translated in James T. O'Connor,
The Gift of Infallibility (San Francisco: Ignatius Press, 2008).
[Vatican I]
we teach and define as a divinely revealed dogma that when the Roman Pontiff speaks EX CATHEDRA, that is, when, in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, he defines a doctrine concerning faith or morals to be held by the whole Church, he possesses, by the divine assistance promised to him in blessed Peter, that infallibility which the divine Redeemer willed his Church to enjoy in defining doctrine concerning faith or morals.
--Chapter 4, Section 9
[Vatican I]
"...the Holy Spirit was promised to the successors of Peter not so that they might, by his revelation, make known some new doctrine, but that, by his assistance, they might religiously guard and faithfully expound the revelation or deposit of faith transmitted by the apostles."
--Chapter 4, Section 6
[Monsignor Gérard Philips, Belgian theologian and primary drafter of Vatican II's Lumen Gentium]
The Divine assistance does not extend to the literary drapery, nor to the theological considerations that surround the definition. Even when the Pope inserts clauses to unfold the deeper meaning of the truth being proclaimed, these expansions do not participate in the charism of infallibility unless they themselves are explicitly formulated as a new, distinct definition. Infallibility attaches to the precise target, not to the surrounding aura of the idea.
--Translated from French
ORIGINAL French Text
L'assistance divine ne s'étend pas à la draperie littéraire, ni aux considérations théologiques qui entourent la définition. Même lorsque le Pape insère des clauses pour déployer le sens profond de la vérité proclamée, ces expansions ne participent pas au charisme de l'infaillibilité, à moins qu'elles ne soient elles-mêmes explicitement formulées comme une nouvelle définition distincte. L'infaillibilité s'attache à la cible précise, non à l'aura qui entoure l'idée.
--Mgr. Gérard Philips, L'Église et son mystère au IIe Concile du Vatican: Histoire, texte et commentaire de la Constitution Lumen gentium, Tome I (Paris: Desclée, 1967), commentary on Chapter III, Paragraph 25.
[Fr. Francis Sullivan]
Vatican I defined that the pope speaks infallibly under the following conditions: "when he speaks ex cathedra, that is, when, acting in the office as the shepherd and teacher of all Christians, he defines, by virtue of his supreme apostolic authority, a doctrine concerning faith or morals to be held by the universal church...There is, in fact, general agreement that the definitions of the immaculate conception by Pius IX and that of the assumption by Pius XII meet all the conditions for defining dogmas of the faith...However, when we look to the past and attempt to determine which papal statements in the course of history have met the conditions for dogmatic definitions, matters are much more complicated. First of all, while it is hardly likely that a modern pope would use the term 'we define' other than in a solemn definition, or fail to use it in such a definition, one cannot presume that this term always had such a specific meaning in documents of the past. In older documents, neither the presence of the term 'we define,' nor it's absence, would be decisive for determining the intention of a pope to speak ex cathedra...the fourteenth century Carmelite bishop, Guido Terreni, who was the first to attribute infallibility to the papal exercise of teaching authority, insisted that the pope would teach infallibly only when he determined a matter of faith for the whole church after having consulted the college of cardinals...The idea that a papal statement should be recognized as a dogmatic definition by the way it has been received, and by the fact that it has been decisive for the faith of the church, might seem to be in conflict with the statement of Vatican I that a papal definition is "irreformable of itself, and not from the consensus of the church." To this objection one can reply that the pope can define as dogma only a truth that has been revealed, and that must therefore be contained at least implicitly in the faith of the church. The eventual failure of any papal doctrine to be received by the church as an article of it's faith would show that that doctrine was not contained in the deposit of faith, and hence was not capable of being defined as dogma.
--Fr. Francis Sullivan "Creative Fidelity" Weighing and Interpreting Documents of the Magisterium." Pgs. 80-82, 88.