How do Catholic and Orthodox theologians reconcile the "infallibility" of the 325 Creed with the semantic reversal of hypostasis in 381?

In both the **Roman Catholic** and **Eastern Orthodox** traditions, the first seven Ecumenical Councils are regarded as being guided by the Holy Spirit, and their dogmatic definitions (the Creeds) are considered infallible. The Catholic catechism states: > *The **infallibility** promised to the Church **is also present in the body of bishops when**, together with Peter's successor, **they exercise the supreme Magisterium," above all in an Ecumenical Council.** When the Church through its supreme Magisterium proposes a doctrine "for belief as being divinely revealed," and as the teaching of Christ, the definitions "must be adhered to with the obedience of faith." **This infallibility extends as far as the deposit of divine Revelation itself**.* The Eastern Orthodox view is the following: > *The Church venerates the **Holy Fathers of the Ecumenical Councils** because Christ has established them as “lights upon the earth,” guiding us to the true Faith. “Adorned with the robe of truth,” the doctrine of the Fathers, based upon the preaching of the Apostles, has established one faith for the Church. The Ecumenical Councils, are the highest authority in the Church. **Such Councils**, **guided by** the grace of **the Holy Spirit**, and accepted by the Church, **are infallible**.* However, a direct comparison between the original Creed of Nicaea (325 AD) and the Niceno-Constantinopolitan Creed (381 AD) reveals what appears to be a reversal of technical terminology.

The Anathema of "hypostasis"

The original 325 Creed concluded with a series of anathemas. The final clause states: > *"But those who say: 'There was a time when he was not'... or that the > Son of God is of a different **hypostasis** (ὑποστάσεως) or substance > (οὐσίας)... the holy catholic and apostolic church anathematizes."* In 325, ***hypostasis*** was synonymous with ***ousia*** (essence). To claim the Son was a different hypostasis than the Father was a mark of Arianism. Yet, by the Council of 381, this anathema was removed, and "Orthodoxy" began to require the confession of three hypostases (the Cappadocian formula). ---------- If these Creeds are ***infallible*** and ***Spirit-led***, how do theologians address the following: - **The Problem of Reversal:** How can a document be "infallible" if a later council must remove an anathema and adopt the very terminology (***different hypostases***) that was previously condemned? - **The Problem of Anachronism:** If the definition of hypostasis was "refined" or changed in 381, then it seems anachronistic to read these later technical distinctions back into the 325 Council, or even into the Biblical text itself. Does this imply that "Orthodoxy" is a moving target of vocabulary rather than a static "deposit of faith"? I am looking for answers that cite reputable theologians regarding how the Church maintains the "immutability" of truth while essentially "correcting" or radically expanding its infallible formulas.