“What seems to me white, I will believe black if the hierarchical Church so defines.”
― St. Ignatius of Loyola
Whatever the Catholic Church teaches, through her Magisterium, is Truth. Because Christ gave Peter the keys, and built the Church upon him, the Church has the authority to proclaim what is and what isn’t true.
In 1582, Pope Gregory XIII declared that the new calendar to use for everyone, would be the Gregorian Calendar. It is the same calendar that we use today, and in fact, every single person (whether Catholic or not) uses this calendar. Catholic monks had a special observatory built so that they could study the stars. During this study, they realized that the Julian calendar was not an accurate representation of how the solar system operated. The Gregorian Calendar fixed this, making the year about 365.25 days long. The Church declared it thus, and it was.
This also shows to, that religion and science can and should work together. There are many other examples of that, but, that is for another discussion.
Since Jesus Christ, is THE Truth, THE Way and THE Life (c.f. John 14:6) and Jesus Christ gave the authority to the Church, the Church has that authority to declare what is and isn’t True, through the Magisterium, that is the teaching aspect of the Church. If the Magisterium taught that 2+2=5, that would be what was true. Though, I don’t think we have to worry about that.
What is truth? Pontius Pilate asked this to Jesus during His trial, during His passion. Pontius Pilate didn’t care what truth was, because he had a majority on his side. Unfortunately, this is what society will try to argue. Truth is what the majority believe. If the majority believe that abortion should be legalized, than let’s legalize it. If the majority believe that gay “marriage” should be legalized, let’s legalize it. If the majority believe in x, then that should be legalized because that is what the majority believe and thus must be true. This is the major problem with a democracy or a republic, that if the majority is wrong, than that wrong becomes legal.
God is the supreme law-giver. He never changes. What He has said in the beginning is true no matter what.