Some of my critics have objected to my use of the word “catholic” to describe my “ecumenism.” I would point out that my use of “catholic” is a perfectly understandable one in English. Dictionaries define the word as “all-inclusive” or “concerning the whole human race” or “universal.” To speak of the church’s catholicity it to affirm that the church includes the people of God ever since Abel, all those united to the Lord Jesus by the Spirit. I would also point out that the alternative definition is pre-loaded so that only the Roman Catholic church qualifies as catholic.
As Calvin said, let’s not quibble over words (he usually said this after quibbling for a few moments, as I’ve done). Some point to the “canon” of Vincent of Lerins as a definition of “catholic”: “Now in the Catholic Church itself we take the greatest care to hold that which has been believed everywhere, always and by all. That is truly and properly ‘Catholic,’ as is shown by the very force and meaning of the word, which comprehends everything almost universally.”
The Vincentian canon, though, is not straightforward, and in the end, it helps me more than my critics.
Recent patristic scholarship has stressed the diversity of teaching and practice. That redoubtable liturgical “splitter” Paul Bradshaw has demonstrated that many of the early chruch practices that are believed to be universal are local ( The Search for the Origins of Christian Worship: Sources and Methods for the Study of Early Liturgy 
In response, it might be said that the liturgical diversity of the early church eventually settled into the fixity of the Latin Mass, or that the spectrum of Christological and Trinitarian opinion was corralled into Nicen0-Constantinopolitan and Chalcedonian orthodoxy. But that doesn’t solve the problem: It’s not the case that Nicene and Chalcedonian Christology was believed ubique , semper , ab omnibus . To match early church history, the canon would have to be revised to read: That is Catholic which is eventually believed ubique ab omnibus , but even if that’s historically accurate, it leaves out the critical semper .
Interpreting Vincent’s canon as a statement about implicit beliefs gives more wiggle room. It might be argued: While patristic writers didn’t express their Marian piety in same way medieval and modern Catholics did, they implicitly affirmed them. Patristic beliefs were the seed from which medieval and modern beliefs grew. That approach creates significant and I think insurmountable problems. Protestants, after all, have often argued that Luther’s views on justification are implicit in Augustine’s doctrines of grace. Who determines which implications stand? And, how do we draw the line between new formulation and new doctrine? Is transubstantiation a fresh formulation of something always and everywhere believed? Or does formulating traditional teaching in Aristotelian categories change the substance of the doctrine? How do we tell the difference between reformulation and new teaching? It often seems a matter of sheer assertion - this is a reformulation and not an innovation because I say so .
Diversity can be overblown. Yet diversity was real, not only in the early church but throughout the medieval period. Once one acknowledges diversity, Vincent’s canon leaves us with a very minimalist definition of “catholic.” If doctrine is catholic if believed everywhere by everyone, then only basic affirmations of Christian faith (Jesus is Lord; Jesus is the Word who is God and with God; the Word became flesh and dwelt among us; the Spirit searches the deep things of God; etc.) qualify. If practices are catholic only if practiced everywhere and always, then we have only a few genuinely catholic Christian rites. Vincent’s canon leaves us with a “catholic” faith that to my eye looks a lot like what I’ve called Reformed catholicity.