It changed a great deal — but not the unchangeable, because the two belong to different categories. The Church has always distinguished dogma, which is irreformable, from discipline and pastoral practice, which can and does change. Vatican II (1962–65) defined no new dogma and pronounced no anathema; the popes who convened and closed it described it as a pastoral council. What it altered — liturgical forms, the language of worship, fasting rules, the manner of engaging the modern world — falls on the changeable side of that line, where the Church has rearranged the furniture many times before.

Why can a council not simply reverse a defined dogma? Because that is not what the Church’s authority is for. Its charism is to guard the deposit, not to edit it. Authentic development, by the ancient test of St. Vincent of Lérins, must unfold “in the same doctrine, in the same sense, and in the same meaning”2 — growth like a child into an adult, the same person throughout, never a swap for a different one. Discipline can flip outright; a defined dogma can only deepen. This is the same machinery that governs whether the Church can change her moral teaching at all.

Now the honest part, because pretending otherwise persuades no one: some conciliar texts read, at least on the surface, in tension with earlier teaching. The declaration on religious liberty sits uneasily beside nineteenth-century condemnations of “liberty of conscience”; the warm tone toward other religions and separated Christians contrasts with the sharper language of earlier centuries. Faithful Catholics debate in good faith how best to reconcile these, and the work of harmonization is genuinely ongoing. A serious answer owns that rather than waving it away.

The Church’s own resolution is the one Benedict XVI named: a “hermeneutic of reform… in the continuity of the one subject-Church”1 set against a “hermeneutic of rupture.” Read the Council as deepening, not breaking; and where a pastoral passage seems to clash with a defined dogma, the dogma governs and the text is read in its light, because the deposit is “held,” not rewritten (2 Thessalonians 2:15). On that reading — the only one compatible with the Church’s indefectibility — Vatican II changed much that could change and nothing that could not. Whether every line has yet been perfectly harmonized is a fair and open question; that the unchangeable went unchanged is not.