Rule of Faith

Rule of Faith February 12, 2023

The words
orthodox and orthodoxy are frequently used in religion and theology. Depending on how the terms are used and the object(s) that they refer to, the meanings of orthodox and orthodoxy can vary widely.

In this paper, I will endeavor to define the standard by which a belief is considered orthodox. I will discuss what is called regula fidei and how it is understood within the Catholic Church. First, however, it is necessary to understand what Catholicism means by orthodoxy.


Composed of two Greek words, orthodox is translated as the straight or right opinion. 

Within the wider Christian world, Orthodox can be used to refer to two different subjects. In the first sense of the word, it is used to identify those churches that are not associated with the Catholic Church but which accept the ancient councils, notably Ephesus and Chalcedon, and which call themselves “the holy, orthodox, catholic, Eastern Church.”

In the second sense of the word, orthodox (again, only when used within a theological context) refers to adherence to certain teachings and creeds promulgated by a religious authority. As such, it is called orthodoxy. It is in this sense of the word that I wish to discuss.

Within Catholicism, orthodoxy is often placed in opposition to the terms heterodoxy and heresy. Heterodoxy is any practice or belief that deviates from the teaching of the Church. 

Heresy takes a precise meaning within Catholicism. It refers to any baptized Christian who denies or doubts any truths that must be believed. Accordingly, four elements constitute formal heresy. A previous valid baptism, which need not have been in the Catholic Church; the external profession of still being a Christian; outright denial or positive doubt regarding a truth that the Catholic Church has proposed as revealed by God; and, finally, the disbeliever must be morally culpable. (See John Hardon’s Modern Catholic Dictionary).

All of this, orthodoxy, heterodoxy, and heresy, can only have meaning when compared to an ideal. Said differently, orthodoxy, heterodoxy, and heresy presuppose a standard. 

What Is Faith? 

In order to understand the need for a standard of faith, it is beneficial to clarify what faith is, or at least what Catholicism means by faith.

In one sense of the word, faith is a supernatural assent to Divine truths. I say supernatural because faith is not a natural part of fallen human nature. Grace can only engender faith. For this reason, faith is called a supernatural virtue. 

However, as Grace is a free and unmerited gift from God, the gift must be accepted. There is, therefore, a free will component to a relationship with God.

Of course, if faith is an assent to truths revealed by God, we presuppose God has revealed Himself to mankind. And that is precisely what Catholicism asserts that the Bible and Divine tradition are. If, then, the person of faith has access to the Bible, why is there any need for an extrinsic rule or standard of faith?

The Need For A Standard

The Bible is the obvious answer to the question of what the standard of faith is. It seems, however, that if the Bible alone were a sufficient standard for faith, there would not be some forty-five thousand Christian denominations worldwide (Center for the Study of Global Christianity). 

Clearly, there is a need for an objective interpreter and standard provider for Sacred Scripture. The need for a standard of faith was evident early in the history of Catholicism, and this role was understood to be filled by the Catholic Church. For this reason, Saint Paul calls the Church “The pillar and foundation of truth.” (1 Timothy 3:15). 

The teaching of the Church’s Doctors reiterates this point. For example, Thomas Aquinas writes, “The formal object of faith is the First Truth as manifested in Holy Scripture and in the Church’s teaching. Hence if anyone does not adhere to an infallible and Divine rule to the Church’s teaching, which proceeds from the Church’s truth manifested in Holy Scripture, such a one has not the habit of faith but holds the truths of faith not by faith but by some other principle.” 

Such a conclusion follows necessarily from any adequate view of the Church as a Divinely constituted body to whose keeping is entrusted the deposit of faith.

Furthermore, since faith is Divine and infallible, the rule of faith must also be Divine and infallible while simultaneously being present in the world. And that is precisely the description and role of the Catholic Church.

Regula Fidei

Regula fidei means rule of faith. More precisely, perhaps, the idea of a rule of faith is intended to suggest an objective standard or norm by which one’s faith is measured and tested. 

Accepting that faith is a necessary condition for salvation and further admitting that such faith requires knowledge of what one must believe in order to be saved, it is evident that an infallible Church is necessary.

The reason why the Catholic Church is the standard of faith lies predominantly in two facts. First, apostolic succession provides an unbroken line from Peter to the Pope. Only the Catholic Church can offer an intact link from the apostles’ teachings to the present day.

Second, as the Church has been commissioned by God to “Go, therefore, and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit, teaching them to observe all that I have commanded you,” the dictate is clear. Under the guidance of the Holy Spirit, the Catholic Church is responsible for teaching what is necessary for our salvation and for maintaining a standard for what must be believed.


If it be true that salvation is predicated upon faith, how important is it that one possess proper knowledge of what one is to believe?

Because the Catholic Church is charged with bringing souls to salvation, the Church must also be responsible for developing and maintaining a rule of faith. 

In this paper, I have sought to explain this rule of faith, known as regula fidei. 

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