The most important dogmatic and polemical work of St. Basil - “Rebuttal to the defensive speech of the evil Eunomius.” The content of this work is determined by the dogmatic provisions of Eunomius, revealed by him in his “Apology”; from this work by Eunomius of St. Vasily cites passages and writes a refutation of them. Treatise of St. Basil in refutation of the heresy of Eunomius is a work that has significantly outlived the time of its writing. The theme touched upon in it and misunderstood by Eunomius is a theme immanent in theology itself. Eunomian no longer exists, the work of Eunomius himself has not survived, but the problem he posed is alive for theological consciousness to this day. This, if we schematize it, is the problem of the knowability of God. Eunomius, Bishop of Cyzicus, was a representative of that strict Arianism that arose in the 50s. IV century, to which Arius himself seemed insufficiently consistent. The founder and first leader of this new Arianism (Anomie) was Aetius. His only gifted student was Eunomius the Cappadocian, who presented in his works a detailed and systematic disclosure of the theological principles of Aetius. Possessing a strictly logical mind, he sharply criticized the Nicene doctrine of consubstantiality, and the influence of his views was so strong that such authoritative church leaders and writers as Basil the Great, Gregory of Nyssa, Apollinaris of Laodicea, Theodore of Mopsuestia had to come out to fight him.