It is a good rule of thumb that an explanation that makes something more obscure and confusing should not be followed. Conversely, the clearer explanation is to be preferred. This rule is also known as Occam's razor, named after the 14th century English philosopher, William of Occam.

The rule is applicable to the debate over the meaning of the Second Vatican Council's teaching that the Body of Christ "subsists in," rather than simply "is," the Catholic Church (Dogmatic Constitution on the Church, n. 8).

Ever since Vatican II's adjournment in December 1965, it has been the common understanding of theologians and various other Catholic scholars, as well as of the cardinals and bishops who constituted the majority of the council, that the council broadened the boundaries of Christ's Church to include Protestants, Anglicans, Orthodox and separated non-Orthodox Christians.

Prior to the council, Pope Pius XII's teaching in his encyclicals Mystici Corporis (1943) and Humani Generis (1950) was considered the common doctrine of the Church, namely, that the Catholic Church and the Body of Christ are "one and the same." Other Christian communities may be related in some way to the Catholic Church, but they are not "members" of that one Church of Christ.

With Vatican II, the concept of membership was set aside and replaced by the concept of "degrees of communion." It is possible, in other words, to be an integral part of the Body of Christ without being in full communion with the Catholic Church.

That is why the council changed the verb from "is" to "subsists in" in article 8 of the Dogmatic Constitution on the Church. It did not want simply to repeat the teaching of Pius XII that the Body of Christ and the Catholic Church are "one and the same." The boundaries of the Church encompass non-Catholic Christians as well as Catholics.

The recent document from the Congregation for the Doctrine of the Faith (CDF) offers a more convoluted interpretation of the change of verbs from "is" to "subsists in" in article 8.

This is how the CDF's accompanying commentary explains the change:

"In fact, precisely because the church willed by Christ actually continues to exist in (subsistit in) the Catholic Church, this continuity of subsistence implies an essential identity between the church of Christ and the Catholic Church."

The commentary continues: "The council wished to teach that we encounter the church of Jesus Christ as a concrete historical subject in the Catholic Church. The idea, therefore, that subsistence can somehow be multiplied does not express what was intended by the choice of the term subsistit. In choosing the word subsistit the council intended to express the singularity and non-'multipliability' of the church of Christ: the church exists as a unique historical reality" (Origins, July 19, p. 138).

Readers should not be quick to accuse themselves of obtuseness if they cannot readily understand what the CDF is saying. Theologians would also have trouble understanding, much less agreeing with, the explanation.

Jesuit Father Francis A. Sullivan, my former professor of ecclesiology at the Pontifical Gregorian University in Rome and now a professor at Boston College, had shed some light on the matter in a letter to America magazine in response to an article the previous month by his fellow Jesuit, Cardinal Avery Dulles, "Vatican II: The Myth and the Reality" (Feb. 24, 2003).

Father Sullivan noted that Cardinal Dulles' argument on the "subsists in" matter was the same as the one advanced by the CDF in its 1985 critique of a book by the Brazilian theologian Leonardo Boff. Sullivan pointed out that in its later document, "Dominus Iesus," the CDF no longer invoked the philosophical notion of subsistence, but translated subsistit according to the basic meaning of the Latin word, which is "to continue to exist."

"Thus, it now explains Vatican II to mean that the church of Christ 'continues to exist fully only in the Catholic Church.' This implies the recognition that the church of Christ continues to exist, but not fully so, in other churches."

This is an interpretation, Sullivan insisted, that is "consistent with the same document's description of the separated Eastern churches as 'true particular churches.' Vatican II teaches that the universal church of Christ exists 'in and out of' the particular churches."

Father Sullivan concluded: "I do not know how we could recognize the Orthodox as 'true particular churches' if we did not also recognize that the universal church of Christ is wider and more inclusive than the Roman Catholic Church."

This is the simpler explanation for the council's change in verbs from "is" to "subsists in." It is also the more accurate.

Fr. Richard McBrien is the Crowley-O'Brien Professor of Theology at the University of Notre Dame.