Infallibility of the Catholic Church

When Christ founded the Catholic Church, he promised it would be guided from failure, and also guided from error. This is referred to as "infallibility". The Catholic Church has also always taught this (based on Christ's promises in Scripture).

Note: there are circumstances that may interfere with infallibility, as described below.

There are two kinds of infallibility; church infallibility and papal infallibility, again based on Our Lord's words in Scripture. See below for a description of each:
 

1. Infallibility of the Church - describes that the Catholic Church is divinely kept from the possibility of error in her definitive teaching on matters of faith and morals. This applies to teaching on faith and morals only. When Our Lord is commanding us with the words in Scripture (below), He is making it clear that He is constantly guiding His Church with this promise of infallibility.

References in Scripture:

• "And I say to thee: That thou art Peter; and upon this rock I will build my church, and the gates of hell shall not prevail against it." Matt 16:18
• "Going therefore, teach ye all nations; baptizing them in the name of the Father, and of the Son, and of the Holy Ghost. Teaching them to observe all things whatsoever I have commanded you: and behold I am with you all days, even to the consummation of the world." Matt 28:19-20
• "But when he, the Spirit of truth, is come, he will teach you all truth. For he shall not speak of himself; but what things soever he shall hear, he shall speak; and the things that are to come, he shall shew you." John 16:13
• "And he said to them: Go ye into the whole world, and preach the gospel to every creature. He that believeth and is baptized, shall be saved: but he that believeth not shall be condemned." Mark 16:15
• "And I will ask the Father, and he shall give you another Paraclete, that he may abide with you for ever. The spirit of truth, whom the world cannot receive, because it seeth him not, nor knoweth him: but you shall know him; because he shall abide with you, and shall be in you." John 14:16-17
   

Church Teaching

• From the First Vatican Council (1870): "the doctrine of faith, which God has revealed, has not been proposed as a philosophical discovery to be improved upon by human talent, but has been committed as a Divine deposit to the spouse of Christ, to be faithfully guarded and infallibly interpreted by her".
   

2. Papal Infallibility - this second type of infallibility in the Catholic Church describes the promise that when the head of the Catholic Church, the Pope, exercises his office on defining a doctrine on faith and morals (ONLY), he possesses infallibility that was promised to the Church.

References In Scripture:

• "And I say to thee: That thou art Peter; and upon this rock I will build my church, and the gates of hell shall not prevail against it." Matt 16:18
• "And the Lord said: Simon, Simon, behold Satan hath desired to have you, that he may sift you as wheat; But I have prayed for thee, that thy faith fail not: and thou, being once converted, confirm thy brethren." Luke 22:31-32
• "When therefore they had dined, Jesus saith to Simon Peter: Simon son of John, lovest thou me more than these? He saith to him: Yea, Lord, thou knowest that I love thee. He saith to him: Feed my lambs. He saith to him again: Simon, son of John, lovest thou me? He saith to him: Yea, Lord, thou knowest that I love thee. He saith to him: Feed my lambs. He said to him the third time: Simon, son of John, lovest thou me? Peter was grieved, because he had said to him the third time: Lovest thou me? And he said to him: Lord, thou knowest all things: thou knowest that I love thee. He said to him: Feed my sheep." John 21:15-17

Church Teaching on Infallibility

• First Vatican Council (1870): "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".
• "This consideration too clarifies the great error of those others as well who boldly venture to explain and interpret the words of God by their own judgment, misusing their reason and holding the opinion that these words are like a human work. God Himself has set up a living authority to establish and teach the true and legitimate meaning of His heavenly revelation. This authority judges infallibly all disputes which concern matters of faith and morals, lest the faithful be swirled around by every wind of doctrine which springs from the evilness of men in encompassing error. And this living infallible authority is active only in that Church which was built by Christ the Lord upon Peter, the head of the entire Church, leader and shepherd, whose faith He promised would never fail. This Church has had an unbroken line of succession from Peter himself; these legitimate pontiffs are the heirs and defenders of the same teaching, rank, office and power. And the Church is where Peter is, and Peter speaks in the Roman Pontiff, living at all times in his successors and making judgment, providing the truth of the faith to those who seek it. The divine words therefore mean what this Roman See of the most blessed Peter holds and has held.
  For this mother and teacher of all the churches has always preserved entire and unharmed the faith entrusted to it by Christ the Lord. Furthermore, it has taught it to the faithful, showing all men truth and the path of salvation. Since all priesthood originates in this church, the entire substance of the Christian religion resides there also. The leadership of the Apostolic See has always been active, and therefore because of its preeminent authority, the whole Church must agree with it. The faithful who live in every place constitute the whole Church. Whoever does not gather with this Church scatters.
  We, therefore, placed inscrutably by God upon this Chair of truth, eagerly call forth in the Lord your outstanding piety, venerable brothers. We urge you to strive carefully and zealously to continually warn and exhort the faithful entrusted to your care to hold to these first principles. Urge them never to allow themselves to be deceived and led into error by men who have become abominable in their pursuits. These men attempt to destroy faith on the pretext of human progress, subjecting it in an impious manner to reason and changing the meaning of the words of God. Such men do not shrink from the greatest insults to God Himself, who cares for the good and the salvation of men by means of His heavenly religion." Encyclical on Faith and Religion by Pope Pius IX, 1846
   

What May Interfere with Infallibility?

• In the event a person either usurps the position of a Pope, or a Pope loses his authority through willful, formal heresy, decisions made by that usurper or heretic would be null and void and infallibility would obviously not apply.
  
  This would be similar to someone claiming they are President of the United States (usurping the position) and trying to pass new laws; any of these new laws would obviously not be binding on citizens of the country.
  
  Attempts to usurp the position of Pope has occurred many times throughout Church history. See the article on "Antipopes" in the Catholic Encyclopedia here:
  
  http://www.newadvent.org/cathen/01582a.htm

Summary

When a Pope exercises his office and solemnly declares a doctrine on faith and morals for the whole Church, he is granted "papal infallibility" through that which Our Lord said in Scripture.

When the Catholic Church allows teachings on faith and morals to continually propagate among the faithful, this teaching is protected from error by the Holy Ghost and is referred to as "the Infallibility of the Church".

These resulting teachings MUST be believed by all Catholics. Refusing to do so is called "heresy" and places one outside the Catholic Church.