The Prophecies of Nostradamus

Nostradamus claimed to base his published predictions on judicial astrology—the astrological 'judgment', or assessment, of the 'quality' (and thus potential) of events such as births, weddings, coronations etc.—but was heavily criticised by professional astrologers of the day such as Laurens Videl for incompetence and for assuming that "comparative horoscopy" (the comparison of future planetary configurations with those accompanying known past events) could actually predict what would happen in the future.

Research suggests that much of his prophetic work paraphrases collections of ancient end-of-the-world prophecies (mainly Bible-based), supplemented with references to historical events and anthologies of omen reports, and then projects those into the future in part with the aid of comparative horoscopy. Hence the many predictions involving ancient figures such as Sulla, Gaius Marius, Nero, and others, as well as his descriptions of "battles in the clouds" and "frogs falling from the sky". Astrology itself is mentioned only twice in Nostradamus's Preface and 41 times in the Centuries themselves, but more frequently in his dedicatory Letter to King Henry II. In the last quatrain of his sixth century he specifically attacks astrologers.

His historical sources include easily identifiable passages from Livy, Suetonius' The Twelve Caesars, Plutarch and other classical historians, as well as from medieval chroniclers such as Geoffrey of Villehardouin and Jean Froissart. Many of his astrological references are taken almost word for word from Richard Roussat's Livre de l'estat et mutations des temps of 1549–50.

One of his major prophetic sources was evidently the Mirabilis Liber of 1522, which contained a range of prophecies by Pseudo-Methodius, the Tiburtine Sibyl, Joachim of Fiore, Savonarola and others (his Preface contains 24 biblical quotations, all but two in the order used by Savonarola). This book had enjoyed considerable success in the 1520s, when it went through half a dozen editions, but did not sustain its influence, perhaps owing to its mostly Latin text, Gothic script and many difficult abbreviations. Nostradamus was one of the first to re-paraphrase these prophecies in French, which may explain why they are credited to him. Modern views of plagiarism did not apply in the 16th century; authors frequently copied and paraphrased passages without acknowledgement, especially from the classics. The latest research suggests that he may in fact have used bibliomancy for this—randomly selecting a book of history or prophecy and taking his cue from whatever page it happened to fall open at.

Further material was gleaned from the De honesta disciplina of 1504 by Petrus Crinitus, which included extracts from Michael Psellos's De daemonibus, and the De Mysteriis Aegyptiorum (Concerning the mysteries of Egypt), a book on Chaldean and Assyrian magic by Iamblichus, a 4th-century Neo-Platonist. Latin versions of both had recently been published in Lyon, and extracts from both are paraphrased (in the second case almost literally) in his first two verses, the first of which is appended to this article. While it is true that Nostradamus claimed in 1555 to have burned all of the occult works in his library, no one can say exactly what books were destroyed in this fire.

Only in the 17th century did people start to notice his reliance on earlier, mainly classical sources.