If you begin to question the validity of the Catholic Church's teachings, then you could be considered a a0.

Answer: Heretic

A heretic is a person who practices heresy. Heresy is mainly used in a religious context in order to describe people who have beliefs that are strongly in opposition to the teachings of a religious organization. In the context of the Catholic Church, heresy only involves the questioning of the Church's principles. Open renunciation of one's religion is called apostasy, while blasphemy is an impious utterance against God or a sacred thing. Throughout history, heresy was strongly punished, sometimes even leading to the death penalty.