What does Ceteris Paribus mean?

In Sacrosanctum Concilium (1963), we read that chant deserves primacy of place in the Roman rite "ceteris paribus." That is rendered in English as "other things remaining equal." This is often seen as a qualifier that discounts the role of chant. Many opponents of chant will shoot back when you quote Vatican II: "But other things are NOT equal."

Well, for years I've looked for evidence from the Council (real contemporary evidence concerning the intentions, not just someone's ex post speculations) as to what precisely was meant by that phrase but not even the most detailed accounts (such as Fr. Ruff's) go into the historical detail.

The best approach, then, is to just accept it at face value. Ceteris Paribus is a common Latin phrase used in scientific literature. Wikipedia (as is often the case) has it precisely right.

It is "to acknowledge, and to rule out, the possibility of other factors which could override the relationship between the antecedent and the consequent."

How does this apply to chant? It means even when chant is not possible, even when there are no skills or singers, or even when the books aren't around, or other conditions prevent chant from being used, that in no way reduces its appropriateness for the Roman Rite. In other word, the phrase reinforces the mandate for chant, pointing out that it is so strong that no conditions that would lead to its absence have the effect of diminishing its preferred position.