Youcat commented through CCC – Question n. 143 - Part I.

YOUCAT Question n. 143 - Part I. Is the Pope really infallible?

(Youcat answer) Yes. But the Pope speaks infallibly only when he defines a dogma in a solemn ecclesiastical act (“ex cathedra”), in other words, makes an authoritative decision in doctrinal questions of faith and morals. Magisterial decisions of the college of bishops in communion with the Pope also possess an infallible character, for example, decisions of an ecumenical council.    

A deepening through CCC

(CCC 891 a) "The Roman Pontiff, head of the college of bishops, enjoys this infallibility in virtue of his office, when, as supreme pastor and teacher of all the faithful - who confirms his brethren in the faith - he proclaims by a definitive act a doctrine pertaining to faith or morals.... The infallibility promised to the Church is also present in the body of bishops when, together with Peter's successor, they exercise the supreme Magisterium," above all in an Ecumenical Council (LG 25; cf. Vatican Council I: DS 3074).    

Reflecting and meditating 

(Youcat comment) The infallibility of the Pope has nothing to do with his moral integrity or his intelligence. What is infallible is actually the Church, for Jesus promised her the Holy Spirit, who keeps her in the truth and leads her ever deeper into it. When a truth of the faith that has been taken for granted is suddenly denied or misinterpreted, the Church must have one final voice that authoritatively says what is true and what is false. This is the voice of the Pope. As the successor of Peter and the first among the bishops, he has the authority to formulate the disputed truth according to the Church’s Tradition of faith in such a way that it is presented to the faithful for all times as something “to be believed with certainty”. We say then that the Pope defines a dogma. Therefore such a dogma can never contain something substantially “new”. Very rarely is a dogma defined. The last time was in 1950.

(CCC Comment)

(CCC 891 b) When the Church through its supreme Magisterium proposes a doctrine "for belief as being divinely revealed" (DV 10 § 2), and as the teaching of Christ, the definitions "must be adhered to with the obedience of faith" (LG 25 § 2). This infallibility extends as far as the deposit of divine Revelation itself  (Cf. LG 25).     

(This question: Is the Pope really infallible? is continued)