Does the Pope teach infallibly ONLY when he speaks ex cathedra?

Question

The Vatican Council (opened on 8 December, 1869) defined as "a divinely revealed dogma" that "the Roman Pontiff, when he speaks ex cathedra — that is, when in the exercise of his office as pastor and teacher of all Christians he defines, by virtue of his supreme Apostolic authority, a doctrine of faith or morals to be held by the whole Church — is, by reason of the Divine assistance promised to him in blessed Peter, possessed of that infallibility with which the Divine Redeemer wished His Church to be endowed in defining doctrines of faith and morals; and consequently that such definitions of the Roman Pontiff are irreformable of their own nature (ex sese) and not by reason of the Church's consent"¹ - Source: Explanation of papal infallibility | Infallibility | New Advent.

^{1. cf. Denzinger 1839 And so We, adhering faithfully to the tradition received from the beginning of the Christian faith, to the glory of God, our Savior, the elevation of the Catholic religion and the salvation of Christian peoples, with the approbation of the sacred Council, teach and explain that the dogma has been divinely revealed: that the Roman Pontiff, when he speaks ex cathedra, that is, when carrying out the duty of the pastor and teacher of all Christians by virtue of his supreme apostolic authority he defines a doctrine of faith or morals to be held by the universal Church, through the divine assistance promised him in blessed Peter, operates with that infallibility with which the divine Redeemer wished that His church be instructed in defining doctrine on faith and morals; and so such definitions of the Roman Pontiff from himself, but not from the consensus of the Church, are unalterable.}

The question is, does the Pope teach infallibly ONLY when he speaks ex cathedra? Are there instances when a Pope has taught infallibly but not precisely as according to the definition by the Vatican Council? If so, what are some examples?

Answer 1

Ex cathedra is the means by which a pope defines dogma. Infallible means "not prone to err."

The First Vatican Council says a pope cannot err when defining dogma. This does not imply he's prone to err when not defining dogma, nor does it mean he must speak ex cathedra to be inerrant.

Encyclicals, for example, are inerrant; otherwise, the Church would demand the faithful to assent to what might contain error, and the Church cannot lead one into error because the Church is indefectible. From Pope Pius XII's Humani Generis:

20. Nor must it be thought that what is expounded in Encyclical Letters does not of itself demand consent, since in writing such Letters the Popes do not exercise the supreme power of their Teaching Authority. For these matters are taught with the ordinary teaching authority, of which it is true to say: "He who heareth you, heareth me";[Luke, X, 16] and generally what is expounded and inculcated in Encyclical Letters already for other reasons appertains to Catholic doctrine. But if the Supreme Pontiffs in their official documents purposely pass judgment on a matter up to that time under dispute, it is obvious that that matter, according to the mind and will of the Pontiffs, cannot be any longer considered a question open to discussion among theologians.

Answer 2

Does the RC Church believe the Pope teaches infallibly ONLY when he speaks ex cathedra (from the chair)?

Roman Catholic teaching affirms that they believe their Pope teaches infallibly Only when he is speaking or teaching from 'the chair', ex cathdra.

RCC has said ONLY when their Pope speaks from the chair, do they believe he will not err in doctrine or moral teaching.

This comes from personally hearing a RCatholic explain ex cathedra reading from RCC approced documentation to me. (this falls within the proof acceptable for support)

As further proof, here is a quote from the Catechism of the Catholic Church;

Pope and Bishops (891)

The Pope is infallible when, as supreme pastor and teacher of the faith, he proclaims by a definitive act a doctrine pertaining to faith and morals.

This infallibility is also present in the body of bishops when, together with the Pope, they exercise the supreme Magisterium, above all in an Ecumenical Council. When the Church proposes a doctrine as Christ's teaching "for belief as being divinely revealed," the faithful must adhere by "the obedience of faith." This infallibility extends to the entire deposit of divine revelation.

This definition is called ex cathedra.

Ex Cathedra

From the Catholic Encyclopedia

Literally "from the chair", a theological term which signifies authoritative teaching and is more particularly applied to the definitions given by the Roman pontiff. Originally the name of the seat occupied by a professor or a bishop, cathedra was used later on to denote the magisterium, or teaching authority. The phrase ex cathedra occurs in the writings of the medieval theologians, and more frequently in the discussions which arose after the Reformation in regard to the papal prerogatives. But its present meaning was formally determined by the Vatican Council, Sess. IV, Const. de Ecclesiâ Christi, c. iv: "We teach and define that it is a dogma Divinely revealed that the Roman pontiff when he speaks ex cathedra, that is when in discharge of the office of pastor and doctor of all Christians, by virtue of his supreme Apostolic authority, he defines a doctrine regarding faith or morals to be held by the universal Church, by the Divine assistance promised to him in Blessed Peter, is possessed of that infallibility with which the Divine Redeemer willed that his Church should be endowed in defining doctrine regarding faith or morals, and that therefore such definitions of the Roman pontiff are of themselves and not from the consent of the Church irreformable."

http://www.catholicity.com/encyclopedia/e/ex_cathedra.html