Tertullian (A.D. c.155–c.240), Latin theologian, an early father of the Christian church. A layman from Carthage, he laid the conceptual and linguistic basis for the doctrine of the Trinity. Though appearing hostile to philosophy (‘What has Athens to do with Jerusalem?’) and to rationality (‘It is certain because it is impossible’), Tertullian was steeped in Stoicism. He denounced all eclecticism not governed by the normative tradition of Christian doctrine, yet commonly used philosophical argument and Stoic concepts (e.g., the corporeality of God and the soul). Despite insisting on the sole authority of the New Testament apostles, he joined with Montanism, which taught that the Holy Spirit was still inspiring prophecy concerning moral discipline. Reflecting this interest in the Spirit, Tertullian pondered the distinctions (to which he gave the neologism trinitas) within God. God is one ‘substance’ but three ‘persons’: a plurality without division. The Father, Son, and Spirit are distinct, but share equally in the one Godhead. This threeness is manifest only in the ‘economy’ of God’s temporal action toward the world; later orthodoxy (e.g. Athanasius, Basil the Great, Augustine), would postulate a Triunity that is eternal and ‘immanent,’ i.e., internal to God’s being. See also MONTANISM, STOICISM , TRINI- TARIANIS. A.E.L.