[Thorndike was an eminent scholar of medieval history and scientific activity in the Middle Ages. His major work is the eight-volume A History of Magic and Experimental Science (1923). In the following excerpt from a revised edition of that work, Thorndike presents an overview of Agrippa 's life and career and offers mixed reviews of On the Uncertainty and Vanity of the Sciences and Occult Philosophy.]

Neither is Henry Cornelius Agrippa of Nettesheim himself to be reckoned of much weight in intellectual history nor is his book on occult philosophy so important a work in the history of magic and experimental science as one might think at first sight. He was not a person of solid learning, regular academic standing, and fixed position, but rather one of those wayward geniuses and intellectual vagabonds so common in the later fifteenth and early sixteenth centuries. In 1509, when not yet twenty-three, he lectured at the university of Dôle on Reuchlin's De verbo mirifico, and had a controversy with a Franciscan who called him a Judaizing heretic on that account. Before this in 1507 he had carried on alchemical experiments at Paris and he resumed them in this same year 1509 at Avignon. From 1511 to 1517 he was in Italy, where in 1515 he lectured at Pavia on the Hermetic philosophy and Marsilio Ficino's commentary on the Pimander. We find him practising alchemy again at Metz in 1518 and 1519, as well as courageously defending a woman who had been hounded down by the mob and inquisitor as a witch. In 1520 he was at Cologne and at Geneva, where he married a second time. Presently he became municipal physician of Fribourg, although he had no medical degree. He never stayed anywhere long, generally contrived to get into trouble wherever he went, and, like Paracelsus, left in a huff. His interest in the doctrines of reformers and Protestants—in 1519 he corresponded with Jacques Lefèvre d'Étaples, in 1525 he possessed books of Luther and Carlstadt—also tended to lay him open to suspicion.

Failing to hold any university teaching position permanently, Agrippa turned to the illicit practice of medicine or to the life of a courtier and office seeker. Having become physician to Louise of Savoy, queen mother of France, while she was at Lyons, he was left behind without pay on her departure, although he was never quite sure whether this was because he had predicted from the stars the success of the duke of Bourbon or because a letter had been brought to her attention in which he told a third person that she abused astrological judgments and was led on by vain hope and superstitious faith. A trip to Paris in an attempt to recover his favor at court was in vain. Next he appears at Antwerp practicing medicine again without a degree during a pestilence. When the plague was over, the local physicians forced him to desist. Birds of a feather flock together, so that we are not surprised to find Agrippa in 1530 addressing to the Grand Council of the Netherlands in session at Malines a defense of Jean Thibault, a contemporary quack and astrologer, against the attack of the physicians of Antwerp, whom he calls envious pigs and defends empiricism against their foolish rational and scholastic medicine. Agrippa would even prefer that mechanical operative medicine which Thessalus said he could teach in six months and which needs no dialectic or mathematics. He asserts that Thibault cured many cases which these doctors had abandoned as hopeless, and that the reason why they did not proceed against him during the epidemic was that they fled from the city at that time.

Agrippa next obtained the post of imperial historiographer, for which he was poorly paid and did little to be paid for. He complained that his work On the Uncertainty and Vanity of the Sciences, now first printed in December, 1530, which aroused against him the faculties of Lou vain and the Sorbonne, also lost him the imperial favor. Meanwhile in 1531 the first book of his Occult Philosophy was published at Antwerp and Paris, a quite inconsistent procedure, since in De incertitudine he had specifically recanted the views expressed in this work. But after he had withdrawn to the protection of the archbishop of Cologne, publication was resumed at that place in November, 1532. The inquisitor, Dominicans and theologians of the university of Cologne made difficulties and delayed publication, however, so that the full text of the three books appeared only in July, 1533, without name of place or printer. John Wier, who later wrote against the witchcraft delusion, was with Agrippa at Bonn in 1535 as pupil and amanuensis. The next year Agrippa again resumed his wanderings and met his death. Gesner, writing in 1545, states that Agrippa, a golden knight and doctor of both laws, had died in Grenoble within a decade or thereabouts reduced to extreme poverty. Thus his troubled, chequered career, marked by no particular distinction but by poverty and bickerings, seemed to end in failure. But he had exerted considerable influence during his lifetime by a fairly wide correspondence with learned men, and, while his medical practice and genius had been far inferior to those of Paracelsus, he had succeeded in publishing his chief works before his death as Paracelsus had failed to do. These works rapidly became well known, perhaps more because they were generally prohibited and because they gave vent to two leading intellectual currents of the time, occultism and scepticism, than because of any intrinsic worth.

Before, however, we come to estimate the contents of Agrippa's De occulta philosophia, let us note further by a thumbing of his letters a few hints that all through his life the occult arts and sciences had been his major interest. Despite the professed recantation in De incertitudine and occasional expressed scepticism as to astrology, he was not untrue to himself in printing, despite strong opposition, as probably his last publication towards the end of his life, this work begun in his youth and of which he had presented a first draft to Trithemius in 1510.

Throughout his life Agrippa was a devotee of the Cabala. On April 30, 1512, he writes from Pa via to father Chrysostom that he sends him the cabalistic book he desired and assures him that "this is that divine science sublimer than all human striving" and that he should conceal in silence in his breast "this wholly sacred and divine art." Or in May, 1525, a friend promises to bring Agrippa "the cabalistic art with many books of Raymond Lull." Or in 1532 Agrippa writes to Bernard, majordomo of cardinal Campeggio, that he counts upon him to obtain a copy of the De arcanis of Petrus Galatinus, the Cabala Samuel, and the ancient Hebrew alphabet. Bernard replies that he is working day and night upon his mystic cabalistic system. He sends greetings to Ludovicus Lucena, from whom he hopes to have more secret light on the significance of the Hebrew letters. Later he writes again from Bologna to Agrippa that he has already sent the Hebrew alphabet attributed to Esdras and is sending from Venice the book of Galatinus. At Padua he met Franciscus Georgius, who has other books in which they are interested but who said that the Cabala of Samuel was disappointing. A Hebrew scholar named Aegidius who died the past month left other books on the Cabala which Bernard will try to procure. All this shows that the unfavorable opinion of the Cabala expressed in De incertitudine was either merely an assumed pose to conform to the sweepingly sceptical character of that work or represented but a passing mood from which in 1532 Agrippa returned again to his former favorite field of study.

On the much less dignified, less difficult, and less divine art of geomancy Agrippa had himself composed a treatise and in 1526 sent to Metz for it and also for the work of Trithemius on steganography. In another letter of April 27, 1530 Agrippa apologizes for his delayed arrival because he knows his correspondent is eager to see a geomantic table of Scepper which he is bringing with him. Apparently Scepper's Assertion of the Faith Against Astrologers did not keep him from lapsing into a lower form of divination. Nor did Agrippa's own previous practice keep him from writing in De incertitudine, after listing earlier geomancies by Hali, Gerard of Cremona, Bartholomew of Parma, and a certain Tundinus, "I too have written a geomancy quite different from the rest but no less superstitious and fallacious or, if you wish, I will even say 'mendacious.'"

Astrological prediction at times irked Agrippa and was called by him an unworthy artifice or idle superstition, but he seems to have done a good deal of it. Rather characteristic is the letter in which he warns a Dominican, Petrus Lavinius, that judicial astrology is a vain superstition and not for a Christian, but at the same time sends him the judgment for which he had asked. He also sent a prognostication to a friend in Chambery "from which you will judge how fine an astrologer I have become"—perhaps an ironic remark—and one to the queen mother of France, Louise of Savoy, and the next year (1527) to the duke of Bourbon. For erecting figures of the sky he preferred Regiomontanus but used the Alfonsine Tables for most other purposes such as the movements and aspects of the stars, although he had tried Bianchini, John de Lineriis, and others. In another letter he calls the Speculum astronomiae of Albertus Magnus a work not praised enough. Late in life he refers to past eclipses, comets, earthquakes, floods and more recent prodigies and signs in the sky as all pointing to one conclusion, and declares that "I predict these things to you, not by doubtful methods of conjecture nor acting under the influence of mental perturbation contrary to true reason but from true arts of vaticination, oracles, prediction and foreknowledge."

Agrippa's friends and correspondents looked on him as a fount of information concerning the occult arts. While municipal physician at Fribourg he instructed a number of prominent citizens in such sciences. In 1527 or 1528 a friend asked Agrippa to send him books of chiromancy with which to amuse himself when exhausted by the din of court life. On December 28, 1532, the majordomo of cardinal Campeggio alluded to a mirror that Agrippa had once showed him in which the dead seemed alive. Another correspondent yearned to see Agrippa, to bathe in the waters of occult philosophy, and to unravel the enigmas and secrets of Picatrix and the Cabala. Another wrote to ask for Agrippa's book of natural magic, which he said he had seen at the university of Pavia. This was what was developed by Agrippa into his three books on occult philosophy. At the time he sent an index or abstract, explaining that it would be sacrilege to publish it to the crowd, and that he reserved the key to it for himself and his friends…. Again in 1527 came another demand for the work.

As for alchemy, in 1526 the curé Brennonius writes from Metz to Agrippa that "our Tyrius," whose vocation was clock-making and avocation alchemy, "has discovered a sweet water in which every metal is easily dissolved by the heat of the sun." It was made from wine, for he separated the four elements and extracted from earth the nature of sulphur. Brennonius, however, had done the same from chelidonia and believed that the water could also be made from anything putrefied—eggs, flesh, bread or herbs of whatever sort. Yet four years later in De incertitudine Agrippa was to declare that alchemy should be prohibited.

Perhaps we can see the reason for Agrippa's persistence in occult practices despite occasional scepticism or religious qualms in the following passage.

Oh! how many writings are read concerning the irresistible power of the magic art, concerning the prodigious images of the astrologers, the marvelous metamorphosis of the alchemists, and that blessed stone which Midas-like turns all to gold or silver at its touch. All which are found vain, fictitious and false as often as they are practiced literally. Yet they are handed down in writings by great and most grave philosophers and holy men whose traditions who will dare to call false? Nay it would be impious to believe that they have written falsehoods in those works. Hence the meaning must be other than the literal sense indicates.

Agrippa's letters also show him interested for a time at least in machines, bridges and military engines, while in De incertitudine he alludes to having once been put in charge of some mines by the emperor and having started to write a book on mining and metallurgy. But he was to a large extent a dabbler and trifler who did not adhere to any given interest for long, just as he did not stay in any one place. Except that always he kept coming back to occult science. Even in De incertitudine he gives information and reveals his knowledge of the field of occult science, devoting a score of its 85 chapters to occult arts and listing past writers on such subjects as chiromancy and natural magic. But it is of course to his De occulta philosophia that we especially turn for his attitude to the occult arts and sciences.

[It] is a disappointing book. It is not a practical manual or even a general theory of the subject but merely a literary description and review, full of what the author doubtless flattered himself was erudite allusion and humanistic eloquence, but vague, totally lacking in precision, and written in the pseudo-Platonic, mooning style of Iamblichus, Ficino and Reuchlin rather than the direct practical tones of Roger Bacon and Albertus Magnus. Cabalistic matter and manner far exceed any natural magic. Despite the title, there is little philosophy to the work, and the author has nothing new to say on his subject. He has read widely in its past literature and is valuable in a scattering way for its bibliography. Yet even in this respect he has failed to achieve anything like an exhaustive or systematic review. Sometimes past writers are misquoted or misunderstood, as when it is asserted that Aquinas in his third book against the Gentiles admits that the human soul can be joined with the celestial intelligence and work marvels. Or the dubious, if not spurious, De fato is cited to show that Aquinas held that works of art receive a certain quality from the stars, whereas really this is just what he explicitly denies in his works of undoubted authenticity. While the book is diffuse and mystical, a much better and meatier encyclopedia of ancient and medieval magic might have been composed than Agrippa's, which seems a hasty rather than thorough piece of work, despite the fact that the author had been so long occupied with it.

Sometimes Agrippa's work may preserve bits from earlier writers that otherwise would not be extant, but this is not often the case. Richard Argentinus, writing in 1563, asserts that Cornelius Agrippa in his Occult Philosophy stole from the libraries of magic of John Torresius of Spain and Bellisarius Petrucius magic characters which he reproduced only faultily because of his ignorance of Syriac.

The work divides into three books corresponding to the three worlds of the cabalists: elemental, celestial or mathematical, and intellectual. Magic is said to embrace the knowledge of all nature. Occult virtues are not of any element but a sequel of a thing's species and form. They are implanted in the species of things by the ideas from the world soul through the stars, and even individuals of the same species may receive different occult virtues from the stars. Sympathy and likeness are the guiding principle or key in the investigation of these occult properties. Agrippa then treats of the distribution of inferior things under the planets and how through natural things and their virtues we can attract the influences of the heavenly bodies and even penetrate to intellectual, demonic and divine forces. The last dozen chapters or so (58-70) of the first book deal with the magical possibilities of the human mind, soul and words, for although these might be regarded as more intellectual than elemental, they are presumably regarded as sunk and bound in this lower world of the elements and body.

The second book is first occupied with the symbolism and virtues of numbers and letters of the alphabet and then with astrology. If there are great occult virtues in natural objects, much more is this the case with numbers which are more purely form and closely related to the celestial bodies and separate substances. Scales are given for the numbers up to twelve. Take two, for example. For the archetype we have the name of God in two letters, in the intellectual world are angel and soul, in the celestial world sun and moon, in the elemental world earth and water, in the microcosm heart and brain, in the inferno Behemoth and Leviathan. Divination by attributing numerical values to letters, astrological images, geomantic figures, and the names of the planets to be employed in magic incantations are other features of the second book.

In an early chapter of the third book Agrippa hints that such ceremonies as excommunicating worms and locusts to save the crops or baptizing bells are relics of the perverse religions of the Chaldeans, Egyptians, Assyrians, Persians and Arabs of the past. But soon he is immersed in cabalistic lore of divine names. The subsequent discussion of demons lacks unity and is a hodge-podge from previous writers, yet by no means covers the various descriptions and classifications of them to be found in classical, patristic and later medieval writers. After some consideration of necromancy and evoking the souls of the dead, we return again to the power of the human soul, to various forms of divination and to ceremonial observances. The work ends with an injunction of secrecy.

Whatever its defects, Agrippa's De occulta philosophia gave a more general presentation of the subject than could be found elsewhere, at least in print. Partly on this account, partly because of its daring enunciation of certain suspect doctrines such as that of a world soul, partly because of advertising which it received by being placed on various lists of prohibited books and Indexes, it found a number of editions and readers during the next two centuries. In 1565 or 1567 was added an apocryphal fourth book of an extreme magical character which appealed further to prurient ears, although Wier defended Agrippa from the attribution of it to him [in his De praestigiis daemonum, 1564]. Agrippa became the hero or villain of legendary tales in the handbooks on witchcraft. Delrio and Boquet tell of a pupil of his at Louvain entering the master's study during Agrippa's absence and opening a book of adjurations. A demon promptly appeared, and the youth died either of fright or because attacked by the demon. When Agrippa returned and saw the dead body, he in turn invoked the demon, whom he forced to enter the corpse, to take a few turns about the square in the presence of other scholars, and then to leave the body which fell to the ground as if the youth died only then, thus clearing Agrippa of suspicion as the cause of his death. But his flight into Lorraine soon followed. Boquet further asserts that Charles V banished Agrippa and two companions from his court and territories.

Rumor was also rife as to the relations between Agrippa and his dog. Bodin in his Démonomanie of 1580 called Agrippa the greatest sorcerer of his time and Wier not only his disciple but valet and servitor, "drinking, eating and sleeping with him, as he confesses, after Agrippa had repudiated his wife." Bodin added that Paul Jovius and others had written that Agrippa's black dog, which he called Monsieur, so soon as Agrippa passed away in the hospital at Grenoble, hurled itself into the river before everyone's eyes and was never seen again. Bodin concludes that Wier says that it was not Satan in the guise of a dog, as well as that he led it after Agrippa on a leash, and that the dog lay between him and Agrippa [in his De la démonomanie des sorciers, 1580]. Wier appears to be slandered in this passage as much as Agrippa or the dog. In the passage to which Bodin alludes, Wier refers to the report that Agrippa's dog was a demon. He states that it was a medium sized black dog called Monsieur with a bitch named Mamselle. Agrippa used to fondle Monsieur excessively, and allowed him beside him at table and in his bed at night, after he had repudiated his wife of Malines at Bonn in 1535. "And when Agrippa and I were eating or studying together, this dog always lay between us." The fact that Agrippa, without leaving his quarters, knew what was going on in foreign parts was due to letters which he received daily from learned men in various regions, but was attributed by popular report to information received from the dog, acting as his familiar demon. Of Agrippa's end Wier says merely that he went from Bonn to Lyons where he was imprisoned a while by Francis I for having written against the queen mother. "Freed by the intercession of certain persons, after some months he fell asleep in the Lord at Grenoble in Dauphiné. At that time I was in Paris" [De praestigiis daemonum, edition of 1583].

Cardan, in connection with the horoscope of Agrippa, gave an estimate of him which is worth repeating. Born poor, he made a pretense to knowledge. Jupiter endowed him with comradery and urbanity to the point of scurrility. Mercury made him ingenious, versatile, mutable, deceitful, tricky and studious. But the tail of the dragon in the degree of the ascendent made him not apt for disciplines. Cardan regarded his De occulta philosophia as full of trifles and falsehoods and deserving to be burned. As for De vanitate scientiarum, Cardan thought its main argument bad, and that Agrippa showed his ignorance in treating things of which he knew nothing. "Yet the book pleases many as chaff does asses" [Opera, 1663]. Tycho Brahe referred to Agrippa as "that most worthless fabricator of vanities" [Astronomiae instauratae progymnasmata: Opera, III, 1916].