|The straight stuff|
In the universal or catholic Church itself, we must make sure that we hold the faith that has been believed everywhere, always, by all. For what is actually and strictly "catholic," or "universal," as the name itself and it's nature imply, is spread out universally. And we will be following this rule if we follow these three things: universality, antiquity, consent. We follow antiquity if we do not depart in any way from the teachings and understandings that were obviously held widely by our holy ancestors and fathers. And we follow consent when we stick to the consensual definitions and determinations of all -- or almost all -- the priests and great teachers in antiquity
...But someone might say, "Then, won't there be any progress in Christ's Church?" On the contrary, there will be as much progress as possible. Only someone who envies humans and hates God would try to stop it. But it must be real progress, not alteration, of the faith. In progress something grows within itself, but in alteration it is transformed into something else. So the intelligence, knowledge, wisdom of individuals and of everyone, of a single person just as much as the whole Church, should grow and make vast and vigorous progress over the ages and centuries. But this will happen within each type of thing, that is in the same teaching and in the same meaning.
Vincent of Lérins (died AD 445)
Commonitory, chapters 2 & 23