Legem credendi lex statuat supplicandi: “The law of prayer determines the law of belief.” This is the ancient saying of Prosper of Aquitaine, which was apparently reversed by Pope Pius XII in Mediator Dei. What does it mean? I have lately encountered the idea that the massive liturgical crisis which we are currently witnessing is due largely to an inversion of the traditional relationship between liturgy and faith. Traditionally, it was the law of prayer, such as that which is in the liturgy, which determined, and was prior to, the law of belief. Aidan Kavanagh writes in his book On Liturgical Theology that faith is consequent upon worship, and not the other way around. Worship is an encounter with the Source of the grace of faith, namely God. Faith is an assent to the revelation given to us by God. As such, faith results from the encounter with God that we experience in worship. The truths of faith expressed in the sacred liturgy are, as it were, the means through which we come into contact with God. We approach them in worship, and in consequence we believe.
At first, I found this to be a somewhat strange understanding of faith. I am always uncomfortable speaking of faith as an “encounter” or an “experience,” because that often smacks of modernism. But the modernistic understanding of faith is as an experience which originates from the sentiments within the Christian himself; whereas the above understanding presents faith as a response to Something that is already out there, an Object that is independent of us; and this is God. God and His eternal truths are prior to our faith; it is our responsibility to assent to Him, with the help of His grace, which is communicated through the liturgy and the sacraments, along with those eternal truths themselves. This assent is faith. To me, this is far from a modernistic understanding of faith, but actually aligns very well the traditional scholastic understanding, as an assent of the mind and will to God’s revelation. It would be a modernistic understanding of faith to consider it as something originating in us. And so it would be modernistic to think of ourselves – mere humans – as having the power to shape our “encounter” or “experience” of God in the liturgy according to a faith which originates in us and is thus as changeable as we are. And it is precisely this tendency whose influence we have witnessed in the recent liturgical reforms.
So it is certainly understandable why certain traditionalists are upset that Pius XII reversed the statement legem credendi lex statuat supplicandi to say legem supplicandi lex statuat credendi. However, I wonder if there is not a legitimate way to understand Pope Pius XII’s intended meaning. On the one hand, as I have just stated, it would be truly modernist to consider the liturgy as something subject to a “faith” which originates in us. On the other hand, can it not be said that the truths of faith themselves are prior to the liturgy? Oftentimes these truths are labelled as “doctrines” or “dogmas” insofar as they are taught by the infallible Church. In this sense, it seems that the liturgy is indeed subject to the law of faith, if by this it is meant that the content of the liturgy is determined by a prior truth. We would have a philosophical problem on our hands if we were to contend that the liturgy itself determines what is and is not true. So there are evidently a couple of different ways to understand what lex credendi means: it could refer to the objective truth that is out there, and thus prior to both the liturgy and our personal assent; or it could refer to our personal assent itself, which is called faith. If the former, the liturgy must indeed be subject to the law of faith and determined by it, and Pius XII’s statement seems to me not to be so unreasonable. If the latter, our faith must indeed be subject to the liturgy. Both of these ways of speaking is theologically legitimate, and they are not in opposition. But when it comes to the use of Prosper of Aquitaine's phrase, we appear to have run up against an equivocation on the “law of faith.”