Fundamental theology is the study of the defense of the Christian religion, particularly concerning the doctrines of the Catholic Church. It is closely related to apologetics, but the term "fundamental theology" is used almost exclusively by Catholics, whereas apologetics refers to the defense of any belief system. It should also not be confused with fundamentalist theology, which is the belief system of any fundamentalist religious group. There are three primary goals of fundamental theology: to demonstrate the validity of theistic belief, to demonstrate the truth of the Christian religion in general, and to demonstrate that the Catholic Church is the specific source of revelation.
Demonstrating the validity of theistic belief goes beyond attempting to prove the existence of some sort of deity. Theistic belief, in this sense, is the belief not only that God exists, but also that God remains involved in human affairs or in the continuation of the universe. Fundamental theologians may defend theism based on a number of philosophical or metaphysical arguments, such as that the existence of order in the universe requires the belief in some Being to order it. They may also include arguments about the nature of the human soul and the moral responsibility to God.
Another goal of fundamental theology is to demonstrate that something of the nature of the divine can be known through revelation, specifically in the revelations of the Christian religion. These arguments commonly revolve around defending the historicity and inspiration of the Bible. An apologist might argue that the coming of Christ fulfilled various prophecies made in the Old Testament hundreds of years beforehand, or that events in the Old Testament such as the story of the flood have archaeological evidence backing them up. Some arguments may be made regarding the moral superiority of the Mosaic Law over other contemporary moral codes. Many theologians have also proposed historical evidence regarding the resurrection of Christ.
Fundamental theology also attempts to prove that the Catholic Church, rather than any other person or institution, is the ultimate source of revelation. Catholics argue that Christianity was intended to be a social structure rather than merely an individual way of life, and that the Catholic Church has the authority to continue speaking on behalf of God. This claim, according to Catholics, has its basis both in Scripture and in early church history. Catholics trace the history of the papacy back to St. Peter, who they say received his authority as head of the Church from Christ himself.