Here is a statement from Sing to the Lord:
73. The “pride of place” given to Gregorian chant by the Second Vatican Council is modified by the important phrase “other things being equal.”69 These “other things” are the important liturgical and pastoral concerns facing every bishop, pastor, and liturgical musician. In considering the use of the treasures of chant, pastors and liturgical musicians should take care that the congregation is able to participate in the Liturgy with song. They should be sensitive to the cultural and spiritual milieu of their communities, in order to build up the Church in unity and peace.
There's nothing particularly wrong with the rendering of the phrase ceteris paribus as "other things being equal." Wikipedia has this helpful point: "Cēterīs pāribus is a Latin phrase, literally translated as 'with other things [being] the same,' and usually rendered in English as 'all other things being equal.' A prediction, or a statement about causal or logical connections between two states of affairs, is qualified by ceteris paribus in order to acknowledge, and to rule out, the possibility of other factors which could override the relationship between the antecedent and the consequent."
Such is the usual view. What seems to be odd in "Sing to the Lord" is the application of the principle, which for this document, seems to be "unless there are reasons to dispense with the rule." It is interpreted as softening, not proving, the rule.
Now, I'm familiar with the phrase mainly from the discipline of economics, and its meaning is very nearly the opposite of what the USCCB says: dispensing with the causal principle because of some intervening consideration does not invalidate the principle. Its purpose is to establish the universality of the principle regardless of changing conditions.
An example: in economics, we say that more units of a good are purchased at a lower price than a higher price, other things being equal. Here is the Law of Demand, which is universal. We add "other things being equal" as a means of making possible a mental experiment. We hold all things still while we change one factor in order to illustrate an effect. If other things were changed, such as taste and a change in demand, the observed effects would be different. But the important factor here is that the principle would STILL apply. Indeed, the reason for the experiment is to underscore the fixed principle.
So it is with chant in liturgy. There might not be any singers who can sing chant. The acoustics might not cooperate. There might be other factors. Whatever they might be, the existence of these changing conditions that somehow make chant unviable under some conditions do not in any way diminish the truth that chant still retains pride of place. In other words, Ceteris Paribus strengthens rather than weakens the place of chant in liturgy.
This is a way of understanding the idea of Ceteris Paribus that is consistent with the usage of it in other contexts. Sing to the Lord has given us no basis, other than assertion, for changing this more common understanding of the term.
