Basil of Caesarea, also called Saint Basil the Great, (330 -379) was the bishop of Caesarea Mazaca in Cappadocia, Asia Minor (modern-day Kayseri, Turkey). St. Basil was born into the wealthy family of Basil the Elder, a famous rhetor,and Emmelia of Caesarea. His parents were known for their piety, and his maternal grandfather was a Christian martyr, executed in the years prior to Constantine I's conversion. The principal theological writings of Basil are his De Spirity Sancto (On the Holy Spirit), a lucid and edifying appeal to Scripture and early Christian tradition (to prove the divinity of the Holy Spirit), and his Refutation of the Apology of the Impious Eunomius, written in 363 or 364, three books against Eunomius of Cyzicus, the chief exponent of Anomoian Arianism. The first three books of the Refutation are his work; the fourth and fifth books that are usually included do not belong to Basil, or to Apollinaris of Laodicea, but probably to Didymus "the Blind" of Alexandria.

St. Basil was one of the most popular of the Greek Fathers amongst the Syrian churches, and his De Spiritu Sancto was twice translated into Syriac. The first version, made in the late fourth/early fifth centuries, survives the three manuscripts of the fifth-seventh centuries and is edited and translated here for the first time. It is a paraphrastic text and so is of theological interest in its own right. Its biblical citations are also noteworthy. The second translation, made in the seventh century, survives only in fragments and these have been collected from florilegia manuscripts and edited in parallel with the Greek text. Introductions to the two volumes explore the Syriac manuscript traditions of this work and their significance, and investigate St. Basil's contacts with Syriac-speaking Christians and the theology of the first Syriac version. Unusually, a detailed orthographic index of textual variants is also included.

This classic exposition of Trinitarian doctrine eloquently sets forth the distinction yet perpetual communion of the divine Persons. Without explicitly calling the Spirit "God, " St Basil demonstrates that He, like the Son, is of the same nature with the Father.

Basil of Caesarea, also called Saint Basil the Great, (329 or 330 - January 1, 379) was the Greek bishop of Caesarea Mazaca in Cappadocia, Asia Minor (modern-day Turkey). He was an influential theologian who supported the Nicene Creed and opposed the heresies of the early Christian church, fighting against both Arianism and the followers of Apollinaris of Laodicea. His ability to balance his theological convictions with his political connections made Basil a powerful advocate for the Nicene position. In addition to his work as a theologian, Basil was known for his care of the poor and underprivileged. Basil established guidelines for monastic life which focus on community life, liturgical prayer, and manual labour. Together with Pachomius he is remembered as a father of communal monasticism in Eastern Christianity. He is considered a saint by the traditions of both Eastern and Western Christianity. Basil, Gregory of Nazianzus, and Gregory of Nyssa are collectively referred to as the Cappadocian Fathers. The Eastern Orthodox Church and Eastern Catholic Churches have given him, together with Gregory of Nazianzus and John Chrysostom, the title of Great Hierarch. His is recognised as a Doctor of the Church in both Eastern Orthodoxy and in the Roman Catholic Church. He is sometimes referred to by the epithet, "revealer of heavenly mysteries" This classic exposition of Trinitarian doctrine eloquently sets forth the distinction yet perpetual communion of the divine Persons. Without explicitly calling the Spirit "God, " St Basil demonstrates that He, like the Son, is of the same nature with the Father.

De Fide and De Spiritu Sancto are the chief dogmatic works of Saint Ambrose of Milan. Composed between 378 and 381 at the request of the Emperor Gratian, they vindicate the Divinity of Christ and of the Holy Spirit against those who would deny them. Saint Ambrose (Aurelius Ambrosius) was bishop of Milan from a.d. 374 to 397 and was one of the most influential ecclesiastical figures of the fourth century. For his brilliant defense of orthodoxy against the Arian heretics, Saint Ambrose is counted as one of the four original Doctors of the Church.