This book is a study of the philosophy of John Scottus Eriugena, the ninth-century Irish philosopher who lived from roughly a.d. 800 to about 877. The whole area of early mediaeval philosophy, in the period stretching from Boethius to Anselm, is still underresearched and poorly understood, except among a few specialists. Nevertheless, it is impossible to understand the great philosophical systems of the High Middle Ages without a detailed knowledge of the tremendous struggle that went on in northern Europe to preserve philosophical and scientific wisdom after the collapse of the Roman administration until the revival of Aristotle in the middle of the twelfth century.

Moreover, the imaginative, speculative system of John Scottus Eriugena is worthy of serious scrutiny in its own right, as a daring and innovative synthesis of Latin logical procedure with the mystical outlook of the Greek Christian Platonists.

Eriugena is a significant figure in many respects. He was a close associate of Charles the Bald, grandson of Charlemagne, a young and shrewd monarch who was an enthusiastic promoter of learning in his kingdom, under whose direction the Carolingian renaissance reached its zenith. Eriugena frequented Charles's court, where he mingled with some of the most important people of his time – the powerful prelate Hincmar, the lover of classics Lupus of Ferrières, the poet and fellow Irishman Sedulius Scottus – and where he became renowned as a magister of the liberal arts.