Addressing his treatise to Giuliano Cesarini, a friend and mentor from his days as a law student at the University of Padua, Nicholas of Cusa in Of Learned Ignorance (also known in English translation as On Learned Ignorance) apologizes for its unusual title, De docta ignorantia (translated into English in 1650 as The Idiot). He explains that he is concerned with theological reasoning and cites many philosophers and theologians in the first of the three books that make up this work. Perhaps the most important is the fifth century church father who wrote as Dionysius the Areopagite (known also as Pseudo-Dionysius or Pseudo-Areopagite). Because no one can know God, Dionysius said in De mystica theologia (c. 500; English translation, 1910), one can know only what God is not. However, one can learn something about God by this via negativa, or “negative way.”

The first book develops the thesis that there is a maximum and a minimum of everything, including knowledge: an absolute extension and contraction. These are transcendent terms, Nicholas explains, so far beyond the human capacity for understanding that they seem paradoxically to coincide. The only satisfactory term for them is God. Because nothing falls outside divine providence, God is the absolute maximum; and because this maximum is somehow contained in creation, God is also the absolute minimum. Humans can comprehend only the finite consequences in between these opposites.

In book 1, Nicholas draws from geometry. He reasons, for example, that a triangle becomes a single line when its apex is extended infinitely. In the process, he finds an interesting analogy of the Trinity which is also unity. Then, in book 2, he turns to astronomy and discusses the movement of heavenly bodies. He challenges the once common view that the universe is a perfect sphere and that heavenly bodies circle the Earth in perfect symmetry. He is not trying to create a Copernican revolution, as some historians suggest, so much as he is saying that all astronomic measurements are relative and only the Creator has an absolute grasp of things. (In this respect, he is actually closer to Albert Einstein and the special theory of relativity.) Finally, in book 3, Nicholas turns to Christian doctrine, meditating on the mission of Jesus Christ from his vantage as a longtime monastic and newly ordained priest. By understanding how God became man, he suggests, one can begin to understand the medial role of human nature, in between nature and divinity.

Like many works of his day, Nicholas’s has a series of short chapters, each with a descriptive heading. He often says he is working by analogy, using geometrical and astronomical figures as “metaphors.” He thus tries to draw his friend, and any subsequent readers, into the sort of thinking that can appreciate what it means to be truly ignorant. As was common at the time, he cites numerous authorities to strengthen his argument. Book 1 takes most of its examples from pagan philosophers in Latin editions. Book 2 continues to draw from pagan writers as it develops the theme of an orderly cosmos, but it ends with a series of biblical paraphrases. Book 3 relies almost entirely on biblical texts, though it may echo some sermons of Nicholas’s fellow countryman Meister Eckhart (Johannes Heinrich Eckhart von Hochheim, 1260-1328).

The term “learned ignorance” has a double meaning. It refers to the ignorance of ostensibly learned men, the pseudoknowledge paraded about by those who know less than they think. (Nicholas knew them well, having served at several German universities.) It also refers to the ignorance that is learned, with pains...