Reasoning steps: Filioque

Verdicts: S15 · Filioque. Shared notes and post-750 development: trinity.

S15.1 (was trinity/T2): The procession of the Holy Spirit

Step S15.1.1: Scripture

John 15:26: the Spirit ‘who proceeds (ἐκπορεύεται) from the Father’, whom the Son ‘will send’. John 16:14–15: the Spirit takes ‘what is mine’. Gal 4:6: ’the Spirit of his Son’. The eternal procession is stated only from the Father; the Son’s role is stated as sending and giving.

Step S15.1.2: Patristic evidence

Gregory Nazianzen: the Spirit ‘proceeds from the Father’. The 381 creed: ‘who proceeds from the Father’. John of Damascus: ‘we do not speak of the Spirit as from the Son’, yet the Spirit is ‘of the Son’ and comes ’through the Son’. Augustine (T3): the Spirit proceeds ‘principally’ from the Father and ‘from the Son also’. Sources: constantinople-i-tri-s1 · gregory-nazianzen-tri-s1 · augustine-tri-s1 · augustine-tri-s2 · john-of-damascus-tri-s1.

Step S15.1.3: Weighing decision

The witness is split. East (Gregory, the 381 creed, John of Damascus): from the Father, through the Son. West (Augustine): from the Father principally and from the Son. The creed’s own wording (381) has ‘from the Father’ only; the later Western insertion of filioque into the creed (Toledo 589; Rome c. 1014) departs from the conciliar text. The later Eastern ‘from the Father alone’ (Photius) sharpens beyond ’through the Son’.

• Confidence: Medium.

Step S15.1.4: Source-proximity weighing

• Scripture (benchmark): John 15:26 states eternal procession from the Father; the Son sends the Spirit (15:26; 16:7) and the Spirit is ‘of the Son’ (Gal 4:6). An eternal procession from the Son is an inference, not a statement. (Scripture confidence: medium)
• Assessment: All patristic evidence is T3–T4; Scripture is the decisive measure and states procession from the Father. Inserting filioque into the creed lacks early and conciliar support; ‘from the Father alone’ as a polemical formula is post-750.