Ever since Thomas Kuhn popularized it with his 1962 book, ''The Structure of Scientific Revolutions,'' the notion of a "paradigm shift" has led to fascinating arguments about whether this or that break with previous scientific understanding counted as one. But that a "paradigm shift" -- like the "shift" from Sir Isaac Newton's cosmology to Albert Einstein's, or the shift from the miasma theory of disease to the germ theory of disease -- is a rupture in continuity is not in much dispute. A "paradigm shift" signals a dramatic, sudden, and unexpected break in human understanding -- and thus something of a new beginning.

So are there "paradigm shifts" in the Church?

We seem to have biblical evidence for one in the first chapter of the Letter to the Galatians, where St. Paul describes, very telegraphically, how he came to grasp an astonishing truth: that the salvation promised to the People of Israel in the covenants with Abraham and Moses had been extended to the Gentiles. Some might find another "paradigm shift" in the first chapter of John's Gospel, in which Jesus of Nazareth is identified as the "Word" who "was in the beginning with God."

These are matters of divine revelation, however, and as the Church has long believed and taught, revelation ended with the death of the last apostle. So the evolution of the Church's understanding of the Gospel over the centuries is not a matter of "paradigm shifts," or ruptures, or radical breaks and new beginnings; it's a question of what theologians call the development of doctrine. And as Blessed John Henry Newman taught us, authentic doctrinal development is organic and in continuity with "the faith once... delivered to the saints" (Jude 1.3). The Catholic Church doesn't do rupture: that was tried 500 years ago, with catastrophic results for Christian unity and the cause of Christ.

So it was unfortunate that Cardinal Pietro Parolin, the Secretary of State of the Holy See, recently described ''Amoris Laetitia,'' Pope Francis's apostolic exhortation on marriage and the family, as a "paradigm shift."

Perhaps Cardinal Parolin meant "paradigm shift" in some other sense than Thomas Kuhn's (although Kuhn's notion of paradigm-shift-as-rupture is the common understanding of the term). Perhaps the cardinal was suggesting that Amoris Laetitia asked all the people of the Church to treat those who have not been married in the Church but who wish to be part of the Catholic community with greater sensitivity and charity (a worthy proposal, although compassion is the norm in the situations with which I'm most familiar). But whatever he may have intended, the cardinal cannot have meant that Amoris Laetitia is a "paradigm shift" in the sense of a radical break with previous Catholic understandings. For the Catholic Church doesn't do "paradigm shifts" in that sense of the term, and the Pope himself has insisted that Amoris Laetitia does not propose a rupture with the Church's settled doctrines on the indissolubility of marriage and worthiness to receive Holy Communion.

Where something similar to a Kuhn-type "paradigm shift" is underway, however, is in the reception of Amoris Laetitia in various local churches -- and this is ominous. The pastoral implementation of Amoris Laetitia mandated in Malta, Germany, and San Diego is quite different than what has been mandated in Poland, Phoenix, Philadelphia, Portsmouth, England, and Edmonton, Alberta. Because of that, the Catholic Church is beginning to resemble the Anglican Communion (itself the product of a traumatic "paradigm shift" that cost John Fisher and Thomas More their heads). For in the Anglican Communion, what is believed and celebrated and practiced in England is quite different from what is believed, celebrated, and practiced in Nigeria or Uganda.

This fragmentation is not Catholic. Catholicism means one Lord, one faith, one baptism, and unity is one of the four distinctive marks of the Church. That unity means that the Church embodies the principle of non-contradiction, such that a grave sin on the Polish side of the Oder River can't be a source of grace on the German side of the border.

Something is broken in Catholicism today and it isn't going to be healed by appeals to paradigm shifts. In the first Christian centuries, bishops frankly confronted and, when necessary, fraternally corrected each other. That practice is as essential today as it was in the days of Cyprian and Augustine -- not to mention Peter and Paul.



- George Weigel is Distinguished Senior Fellow of the Ethics and Public Policy Center in Washington, D.C.