THE THEOLOGICAL CONTRIBUTION OF ST. BASIL THE GREAT AND ST. GREGORY THE THEOLOGIAN TO THE FORMATION AND DEVELOPMENT OF THE TERMINOLOGY “OUSIA” AND “HYPOSTASIS” IN THE POST-NICENE PERIOD

Abstract

The article explores the theological contributions of St. Basil the Great and St. Gregory the Theologian to the formation and development of the terminology “ousia” (essence) and “hypostasis” (person) during the post-Nicene period (4th century), a time when the Christian Church faced the urgent need to clarify theological concepts to safeguard the doctrine of the Holy Trinity. Through a detailed analysis of their works—such as St. Basil’s “Letters” and “On the Holy Spirit,” and St. Gregory’s “Theological Orations”—alongside testimonies from church historians (Eusebius of Caesarea, Sozomen, Theodoret) and contemporary Ukrainian scholarship (H. Lubachivskyi, V. Smih), the study demonstrates that the Cappadocian Fathers established the formula “μία οὐσία – τρεῖς ὑποστάσεις” (“one ousia – three hypostases”), which became the cornerstone of Orthodox Trinitarian and Christological thought. The article examines the terminological challenges following the Council of Nicaea (325 CE), where ambiguity fueled heresies like Arianism and Sabellianism, and highlights how St. Basil, using philosophical analogies (e.g., human nature), distinguished between the shared divine essence and individual modes of existence, while St. Gregory blended apophatic (God’s essence is beyond comprehension) and cataphatic (God is known through His actions) approaches, emphasizing the unity of the Godhead in love. Their terminology underpinned the doctrine of the Council of Chalcedon (451 CE), which affirmed the unity of Christ’s hypostasis with two natures. Today, Ukrainian theology leverages the Cappadocians’ legacy to revitalize theological education, integrate patristic concepts into liturgical practices, and foster interdenominational dialogue, underscoring the enduring relevance of their work [Basil the Great, 2010, p. 305–306; Gregory the Theologian, 2010, p. 308–310; Lubachivskyi H., 2019, p. 212–215; Terminological Guide, 2005, p. 302–311].