Isaia 53,8 against Nicaea homoousios.The Sirmio synod in 357: roots and reactions. Irenaeus of Lyons uses Is 53,8 as an epistemological defence of the generation of the Word from God, against Gnostic speculations on the subject.We find this epistemological use of the verse again in the 4th century on the various sides of the Arian controversy. Here we focus on its presence in the anti- Nicene synod of Sirmium in 357 and on the Latin responses, on the Nicene side, to it: Phoebadius of Agen, Hilary of Poitiers and Marius Victorinus. Hilary, unlike the others, responds to the Homoean use of the Irenean exegetical argument by recovering its fundamental apophatic instance. Hilary’s response can still offer theology useful distinctions for a healthy posture that respects the Trinitarian mystery.