The Renaissance was the golden age of belief in magic, defined as an organized science focused on the understanding and practical application of observed phenomena that cannot be explained by conventional, rationalistic philosophy and science but nevertheless are confirmed by actual experience. Thus magic was conceived as a sort of supreme science, embracing not only the rationally explicable aspects of experience but also all sorts of phenomena which were believed to have real existence but seemed to violate the rules of reason. The word magic served as a blanket term for a whole bundle of what modern thought would label pseudosciences. Astrology, one of those pseudosciences, sought to discover, understand, and make use of the physical and spiritual influences exerted by the stars and planets on the earth. It was closely linked to magic because the influence of the stars was one of the basic forces that must be taken into account by anyone who wanted to control the occult powers that were the basis of magic.
What is most significant about the place of magic and related subjects like astrology and alchemy in the civilization of the Renaissance is that the attraction of these subjects was not limited to culturally and intellectually marginal groups and individuals but was taken with great seriousness by some of the leading minds of the age. There was a popular, unintellectual magic that consisted of nothing but collections of spells, enchantments, and substances, often used to cure disease or to gain control over individuals — for example, to provoke love. But both magic and astrology also were serious subjects, studied by learned and intelligent scholars.
Many of those who studied magic attempted to establish a clear distinction between "natural magic," the study of phenomena that could be observed by the senses but could not be rationally explained by traditional Aristotelian science (the action of a magnet on iron was often used as an example) and "spiritual magic," magical operations that involved words and incantations and hence seemed to involve bringing intelligent spiritual beings into action to assist the magician. Use of spiritual forces seemed dangerous since those forces might well be evil demons seeking to lure the soul of the magus (practitioner of magic) to its damnation. Although some magicians tried to distinguish between use of good demons and use of evil demons, any demonic or spiritual magic was risky since evil demons were deceitful and might disguise themselves as good ones. Attempts to practice "astral magic," that is, the application of occult forces shed upon the earth by the celestial bodies, were also debatable, since some of these presumed forces seemed material and natural (the use of sunlight to bleach linen, for example) while others were thought to be spiritual and hence involved all the objections to practicing demonic magic.
The credibility of magic was enhanced by the fact that belief in magic and astrology had also been an important aspect of the classical civilization that the Renaissance intellectuals admired. Hence study of ancient texts — or of postclassical texts that claimed to be ancient—reinforced interest in the occult sciences. The greatest support for the intellectual credibility of magic was the rediscovery of ancient Neoplatonic texts that provided a philosophical basis for magic. The crucial step toward an effort to transform magic from crude charms and rituals employed by unlearned sorcerers into an intellectually defensible science was the work of the Florentine philosopher Marsilio Ficino in translating the works not only of Plato himself but also of the Hellenistic and Roman Neoplatonists. The exaggerated emphasis on the spirit-world found in some of these texts stimulated interest in spiritual magic, while Ficino himself, a physician as well as a philosopher, sought to incorporate traditional material substances into a system of thought that embraced both natural magic and spiritual magic. His treatise De vita coelitus comparanda / On Drawing Life-forces down from the Heavens, the last part of a larger work called De vita / On Life (1489), provided a philosophical basis for study of magic as a real science. Despite his effort to be cautious and orthodox, Ficino practiced a kind of demonic magic that probably violated the laws of both the church and the Roman state. He regarded magic as the supreme form of philosophy and traced its origins through an unbroken chain of enlightened souls from the Persian sage Zoroaster and the Egyptian sage Hermes Trismegistus through the Greek philosopher Pythagoras to Plato, and from Plato through the Neoplatonic tradition down to his own rediscovery of the Neoplatonic and Hermetic writings.
A second major Renaissance influence on this effort to make magic respectable by giving it ancient sources and a philosophical foundation was Ficino's friend Giovanni Pico della Mirandola. He also emphasized the dangers of using occult powers for corrupt and worldly goals and taught that only the properly prepared and spiritually oriented soul could avoid diabolical traps. His interest in Jewish Cabala involved an effort both to justify magical learning and to provide a set of symbols, the letters of the Hebrew alphabet and the words of Hebrew Scripture, that could be safely used for magical works because of its scriptural foundation. Pico differed from Ficino and from nearly all other scholars of philosophical magic by his rejection of astrology. In fact, he produced a tract, Disputationes adversas astrólogos / Disputations against the Astrologers (posthumously published in 1513) that challenged the theoretical basis for both scholarly and popular belief in astrology.
The interest in magic (and usually also in astrology) aroused by these Florentine Neoplatonists continued into the 16th and 17th centuries. The German scholar Agrippa von Nettesheim, who studied Ficino's works closely and was influenced by Pico's writings to study Jewish cabalistic books, produced the most comprehensive attempt to systematize all the magical learning of antiquity and the Middle Ages and enrich it with doctrines of Ficino and Pico. His De occulta philosophia libri tres / Three Books of Occult Philosophy (1533) was republished several times later in the century. Another influential book on magic was De naturalium effectuum causis sive de incantationibus / On the Causes of Natural Phenomena, or On Incantations by the Aristotelian philosopher Pietro Pomponazzi. He solved the problem of demonic magic by dismissing all possibility of action by spiritual agents on material substances. He described a magical science that involved only the action of natural agents on material objects. He attributed a major role to astrological influences, which he likewise redefined to eliminate the possibility of spiritual forces, reducing celestial influences to the purely material level. Later authors who wrote on magical themes included three late Renaissance philosophers, Giordano Bruno, Giambattista della Porta, and Tommaso Campanella. These and other occultist philosophers drew most of their underlying magical ideas from Ficino and Pico. Sharply different from all the others was the German physician Paracelsus, who borrowed some ideas from the Florentine Platonists but also drew on materials provided by the uneducated classes, including alchemy, metallurgy, and popular theology.
The shaky foundations of magic's claim to be a genuine science were evident to the English philosopher-scientist Francis Bacon, who tried without much success to reform and preserve whatever was good and useful in magic while purging the science of its ancient philosophical sources and attempting to base it on empirical knowledge. Even more destructive was the work of a number of mathematicians and scientists brought together in Paris by the monk Marin Mersenne, a translator of Galileo and an associate of both René Descartes and Blaise Pascal; by the 1630s he and his friends had essentially abandoned the basic magical premise that nature is full of spirits and can be understood and controlled by spiritual forces. Henceforth, throughout the 17th century, magic gradually lost its Renaissance aura of intellectual respectability and came to be dismissed by the educated classes as mere superstition or fraud.
Historical Dictionary of Renaissance. Charles G. Nauert. 2004.