The work by Tertullian in which the doctrine of the Spirit is most fully brought out; in which, in fact, He is first expressly named God, is the Adversus Praxean. It was written after his secession from the Church, and Hilary, upon whom it had more influence than any other of Tertullian’s writings, may have suspected that this teaching was the expression of his Montanism rather than a legitimate deduction from Scripture, and so have been misled by over caution. He may also have been influenced by such Biblical passages as Rev. xiv. 1, where the Spirit is unnamed.