Life
Eriugena was highly proficient in Greek, which was rare at that time in mainland Europe, and was thus well-placed for translation work. Although he was born in Ireland, he later moved to France (about 845) and took over the Palatine Academy at the invitation of King Charles the Bald. The reputation of this school seems to have increased greatly under Eriugena's leadership, and the philosopher himself was treated with indulgence by the king. William of Malmesbury's amusing story illustrates both the character of Eriugena and the position he occupied at the French court. The king having asked, Quid distat inter sottum et Scottum? (What separates a sot from a Scot?) Eriugena replied, Mensa tantum (Only a table).

He remained in France for at least thirty years. At the request of the Byzantine emperor Michael III (ca. 858), John undertook some translation into Latin of the works of Pseudo-Dionysius and added his own commentary. He was thus the first to introduce the ideas of Neoplatonism from the Greek into the Western European intellectual tradition, where they were to have a strong influence on Christian theology.

The latter part of his life is involved in total obscurity. The story that in 882 he was invited to Oxford by Alfred the Great, that he labored there for many years, became abbot at Malmesbury, and was stabbed to death by his pupils with their styli, is apparently without any satisfactory foundation, and doubtless refers to some other Johannes. Eriugena in all probability never left France, and Haurau has advanced some reasons for fixing the date of his death about 877. From the evidence available it is impossible to determine whether he was a cleric or a layman, although it is difficult to deny that the general conditions of the time make it more than probable that he was a cleric and perhaps a monk.

Works
His work is largely based upon Saint Augustine, Pseudo-Dionysius and the Cappadocian Fathers, and is clearly Neoplatonist. He revived the transcendentalist standpoint of Neoplatonism with its "graded hierarchy" approach. By going back to Plato, he revived the nominalist-realist debate, which was eventually to translate into the fundamental struggle between entrenched dogma and scientific rationalism, and which came ultimately to undermine the power and authority of the Church in more recent centuries.

The first of the works known to have been written by Eriugena during this period was a treatise on the Eucharist, which has not come down to us. In it he seems to have advanced the doctrine that the Eucharist was merely symbolical or commemorative, an opinion for which Berengar of Tours was at a later date censured and condemned. As a part of his penance, Berengarius is said to have been compelled to burn publicly Eriugena's treatise. So far as we can learn, however, Eriugena's orthodoxy was not at the time suspected, and a few years later he was selected by Hincmar, archbishop of Reims, to defend the doctrine of liberty of will against the extreme predestinarianism of the monk Gottschalk(Gotteschalchus).

The treatise De divina praedestinatione, composed on this occasion, has been preserved, and from its general tenor one cannot be surprised that the author's orthodoxy was at once and vehemently suspected. Eriugena argues the question entirely on speculative grounds, and starts with the bold affirmation that philosophy and religion are fundamentally one and the same. Even more significant is his handling of authority and reason. The work was warmly assailed by Drepanius Florus, canon of Lyons, and Prudentius, and was condemned by two councils: that of Valence in 855, and that of Langres in 859. By the former council his arguments were described as Pultes Scotorum ("Scots porridge") and commentum diaboli, ("an invention of the devil").

Translation of Ps. Dionysius
Eriugena's next work was a Latin translation of Dionysius the Areopagite undertaken at the request of Charles the Bald. This also has been preserved, and fragments of a commentary by Eriugena on Dionysius have been discovered in manuscript. A translation of the Areopagite's pantheistical writings was not likely to alter the opinion already formed as to Eriugena's orthodoxy. Pope Nicholas I was offended that the work had not been submitted for approval before being given to the world, and ordered Charles to send Eriugena to Rome, or at least to dismiss him from his court. There is no evidence, however, that this order was attended to.

Periphyseon
Eriugena's great work, De divisione naturae (Periphyseon), which was condemned by a council at Sens by Honorius III (1225), who described it as "swarming with worms of heretical perversity," and by Gregory XIII in 1585, is arranged in five books. The form of exposition is that of dialogue; the method of reasoning is the syllogism. Natura is the name for the universal, the totality of all things, containing in itself being and non-being. It is the unity of which all special phenomena are manifestations. But of this nature there are four distinct classes (1) that which creates and is not created; (2) that which is created and creates; (3) that which is created and does not create; (4) that which neither is created nor creates. The first is God as the ground or origin of all things, the last is God as the final end or goal of all things, that into which the world of created things ultimately returns. The second and third together compose the created universe, which is the manifestation of God, God in process, Theophania. Thus we distinguish in the divine system beginning, middle and end; but these three are in essence one; the difference is only the consequence of our finite comprehension. We are compelled to envisage this eternal process under the form of time, to apply temporal distinctions to that which is extra- or supra-temporal.

Influence
Eriugena's work is distinguished by the freedom of his speculation, and the boldness with which he works out his logical or dialectical system of the universe. He marks, indeed, a stage of transition from the older Platonizing philosophy to the later scholasticism. For him philosophy is not in the service of theology. The above-quoted assertion as to the substantial identity between philosophy and religion is repeated almost word for word by many of the later scholastic writers, but its significance depends upon the selection of one or other term of the identity as fundamental or primary. For Eriugena, philosophy or reason is first, primitive; authority or religion is secondary, derived.

His influence was greater with mystics than with logicians, but he was responsible for a revival of philosophical thought which had remained dormant in western Europe after the death of Boethius.