Guide Us in All Truth (C19E6)
Jesus at the Last Supper tells his disciples, “the Father will send [the Holy Spirit, who] will teach you everything and remind you of all that I told you.” John 14. We have a great promise from Jesus that we are not just left up to our own human reason, but guided by the Holy Spirit. And if Jesus rose from the dead, then his promises are true. The best explanation is from the Catechism of the Catholic Church paragraphs 888-892
4 ways of infallible teaching magisterium
First, the most exciting EXTRODINARY (not in a good way) act of Infallible teaching magisterium proclamation from the pope to “by a definitive act a doctrine pertaining to faith or morals.” Ex Cathedra (from the chair of Peter).
Example: Pope Pius IX in 1854 proclaimed Ex Cathedra to define that “Mary was, from the first moment of her conception […] preserved immune from all stain of original sin” (Ineffabilis Deus) CCC 490-493
Second, Ecumenical Council. An act of Supreme Magisterium where the bishops acting together with the pope meet and decide on matters of faith and morals.
Example: Council of Nicaea, defining Jesus full humanity and divinity. CCC 464-469
Third, unanimous agreement of the bishops with the pope as the ordinary and universal magisterium.
Example: Before Pope John Paul the Great wrote Evangelium Vitae he surveyed all the bishops and found unanimous agreement that murder, willed abortion, and euthanasia were immoral.
Example: Pope Pius IX references this sense (although not explicitly) often in his justification for declaring the Immaculate Conception in Ineffabilis Deus.