Thought

Dee was an intensely pious Christian, but his Christianity was deeply influenced by the Hermetic and Platonic-Pythagorean doctrines that were pervasive in the Renaissance. He believed that number was the basis of all things and the key to knowledge, that God's creation was an act of "numbering". From Hermeticism, he drew the belief that man had the potential for divine power, and he believed this divine power could be exercised through mathematics. His cabalistic angel magic (which was heavily numerological) and his work on practical mathematics (navigation, for example) were simply the exalted and mundane ends of the same spectrum, not the antithetical activities many would see them as today. His ultimate goal was to help bring forth a unified world religion through the healing of the breach of the Catholic and Protestant churches and the recapture of the pure theology of the ancients.

Reputation and significance

About ten years after Dee's death, the antiquarian Robert Cotton purchased land around Dee's house and began digging in search of papers and artifacts. He discovered several manuscripts, mainly records of Dee's angelic communications. Cotton's son gave these manuscripts to the scholar Méric Casaubon, who published them in 1659, together with a long introduction critical of their author, as A True & Faithful Relation of What passed for many Yeers between Dr. John Dee (A Mathematician of Great Fame in Q. Eliz. and King James their Reignes) and some spirits. As the first public revelation of Dee's spiritual conferences, the book was extremely popular and sold quickly. Casaubon, who believed in the reality of spirits, argued in his introduction that Dee was acting as the unwitting tool of evil spirits when he believed he was communicating with angels. This book is largely responsible for the image, prevalent for the following two and a half centuries, of Dee as a dupe and deluded fanatic.

Around the same time the True and Faithful Relation was published, members of the Rosicrucian movement claimed Dee as one of their number. There is doubt, however, that an organized Rosicrucian movement existed during Dee's lifetime, and no evidence that he ever belonged to any secret fraternity. Dee's reputation as a magician and the vivid story of his association with Edward Kelley have made him a seemingly irresistible figure to fabulists, writers of horror stories and latter-day magicians. The accretion of false and often fanciful information about Dee often obscures the facts of his life, remarkable as they are in themselves.

A re-evaluation of Dee's character and significance came in the 20th century, largely as a result of the work of the historian Frances Yates, who brought a new focus on the role of magic in the Renaissance and the development of modern science. As a result of this re-evaluation, Dee is now viewed as a serious scholar and appreciated as one of the most learned men of his day.

His personal library at Mortlake was the largest in the country, and was considered one of the finest in Europe, perhaps second only to that of de Thou. As well as being an astrological, scientific and geographical advisor to Elizabeth and her court, he was an early advocate of the colonization of North America and a visionary of a British Empire stretching across the North Atlantic.

Dee promoted the sciences of navigation and cartography. He studied closely with Gerardus Mercator, and he owned an important collection of maps, globes and astronomical instruments. He developed new instruments as well as special navigational techniques for use in polar regions. Dee served as an advisor to the English voyages of discovery, and personally selected pilots and trained them in navigation.

He believed that mathematics (which he understood mystically) was central to the progress of human learning. The centrality of mathematics to Dee's vision makes him to that extent more modern than Francis Bacon, though some scholars believe Bacon purposely downplayed mathematics in the anti-occult atmosphere of the reign of James I. It should be noted, though, that Dee's understanding of the role of mathematics is radically different from our contemporary view.

Dee's most long-lasting practical achievement may be his promotion of mathematics outside the universities. His "Mathematical Preface" to Euclid was meant to promote the study and application of mathematics by those without a university education, and was very popular and influential among the "mecanicians" the new and growing class of technical craftsmen and artisans. Dee's preface included demonstrations of mathematical principles that readers could perform themselves.

Dee was a friend of Tycho Brahe and was familiar with the work of Copernicus. Many of his astronomical calculations were based on Copernican assumptions, but he never openly espoused the heliocentric theory. Dee applied Copernican theory to the problem of calendar reform. His sound recommendations were not accepted, however, for political reasons.

He has often been associated with the Voynich Manuscript. Wilfrid M. Voynich, who bought the manuscript in 1912, suggested that Dee may have owned the manuscript and sold it to Rudolph II. Dee's contacts with Rudolph were far less extensive than had previously been thought, however, and Dee's diaries show no evidence of the sale.