Astrological images from Thomas Aquinas to Marsilio Ficino

Can an image engraved on a stone receive power from the heavens? For the philosophers of the Middle Ages and the Renaissance this was no idle question. Around astrological images, that is, figures of planets and constellations engraved or cast at chosen moments, a debate developed that lasted for centuries and involved theologians, astronomers and humanists, from Thomas Aquinas to Marsilio Ficino, with very different positions.

The Arabic sources and the problem of figures

Texts on images reached Europe with the translations from Arabic of the twelfth century. Among the best known was the De imaginibus attributed to Thābit ibn Qurra, a scholar from Harran active in Baghdad who died in 901, translated into Latin by John of Seville and, in another version, by Adelard of Bath. The treatise described images to be made under particular celestial configurations in order to obtain various effects.

The philosophical question was whether a figure had any natural efficacy in itself. A stone possessed virtues of its own, recognised by the long tradition of the lapidaries. But could the engraved form, the drawing of a lion or a scorpion, add anything to those virtues? Opinions divided on this point, with important consequences for the moral and religious judgement of the use of images.

The verdict of Aquinas and of the Speculum astronomiae

Thomas Aquinas addressed the subject in the Summa contra gentiles. In his view figures have no natural power, because an artificial form does not change the nature of the material. If images produce effects, this happens because the engraved signs and characters work as messages addressed to separate intelligences, that is, to demons. Hence his clear condemnation of images accompanied by inscriptions and characters.

More nuanced is the position of the Speculum astronomiae, a thirteenth-century treatise traditionally attributed to Albertus Magnus, an attribution now debated. The author distinguishes three kinds of images: the abominable ones, which require fumigations and invocations; the detestable ones, which use characters and names; and finally purely astronomical images, which would rely only on the virtue of the heavens and which he considers permissible.

Ficino's cautious synthesis

In 1489 Marsilio Ficino published De vita libri tres in Florence. The third book, De vita coelitus comparanda, discusses images at length, drawing on Aquinas, Plotinus and the Arabic sources. Ficino wavers between interest and caution: he admits that materials and the celestial moment may play a part, but prefers to rely on music, scents, colours and way of life, means that he considered safer and more in keeping with nature.

Despite his precautions, the book aroused suspicion in circles of the Roman curia. Ficino replied with an apology, stressing that he had merely reported the opinions of others and that he submitted everything to the judgement of the Church. The case shows how thin the line was between natural philosophy and forbidden practice, and how skilfully humanists had to manoeuvre between intellectual curiosity and orthodoxy.

The debate on astrological images is one of the most interesting chapters in European intellectual history. It touches on the relationship between form and matter, sign and meaning, natural science and religion. The answers of Aquinas, of the Speculum and of Ficino show three different attitudes, which continued to confront one another until the Scientific Revolution and the birth of a new idea of nature.