Eriugena as depicted in Honorius Augustodunensis' Clavis physicae (12th century).
Eriugena was probably educated in Ireland.
By 851 the reputation for learning Eriugena had acquired was sufficient for his being asked to give his views on the dispute that had arisen over the interpretation of Augustine’s teaching on predestined grace. In his reply, Depraedestinatione, he revealed a critical understanding of the relevant texts of Augustine and adopted his precept that the seven liberal arts should be applied to the solution of theological problems. He also gave early evidence of a knowledge of Greek that was to become exceptional, if not unique, in ninth-century Europe.
Eriugena specifically attributed to an inadequate understanding of Greek and the liberal arts the failure of his contemporaries to understand Augustine’s teaching and made these two disciplines the principal subjects in the curriculum of the palace school at Laon, over which he presided with the assistance of his fellow countryman Martin. Here he restored to the arts their ancient classical function of propaedeutic to philosophy and theology. He taught them through the medium of a book that had been forgotten since the end of the ancient world, the De nuptiis of Martianus Capella, and used another forgotten work, Boethius’ Consolation of Philosophy, for more advanced studies. To these texts he and his colleagues appended commentaries that, although not certainly extant in complete form today, established the matter and method of teaching in schools throughout Europe from the ninth to the twelfth centuries. Eriugena and his colleagues at Laon thus founded the educational system of the later Middle Ages and perpetuated the Carolingian renaissance.
The fame of the Greek scholarship at Laon was such that Charles the Bald commissioned Eriugena to translate into Latin the treatises of the pseudo-Dionysius and the First Ambigua of Maximus the Confessor. These labors, to which he added for his own purposes translations of the Quaesliones ad Thalassium of Maximus and the De hominis opificio of Gregory of Nyssa, occupied the years between 860 and 864. They brought Eriugena, already inclined toward Platonism by his reading of Augustine, into direct contact with the fully developed post-Plotinian Neoplatonism which had been absorbed by the Greek Fathers but until then had been a closed book for the Latin West.
The immediate consequence of this contact was the composition, between 864 and 866, of Eriugena’s greatest work, the Periphyseon or De divisione naturae, in which the Western and Eastern forms of Neoplatonism are synthesized within a Christian context. In his subsequent writings - the Expositiones super Ierarchiam caelestem, his commentary on St. John’s Gospel (of which only three fragments survive), and his homily on St. John’s Prologue - he enunciates the theories of the Periphyseon with greater conviction and expresses them in more precise language, but nowhere does he change or abandon them.
These last works were written between 866 and 870, after which nothing further is known of Eriugena; his end is as obscure as his beginning.