Vis imaginativa: the power of imagination

“Fortis imaginatio generat casum”, a strong imagination produces the event. So Michel de Montaigne opens, in the first book of the Essays published in 1580, the chapter devoted to the power of imagination, attributing the saying to the learned. The motto sums up a very widespread conviction in Renaissance philosophy and medicine: the imagination is not only the faculty of producing mental images, but an active power, capable of altering the body of the person who imagines and, according to some, even the surrounding world.

Ancient and medieval psychology

In Aristotelian psychology phantasia occupies an intermediate position between the senses and the intellect: it preserves the images of perceived things and presents them to reason. The Arab philosophers developed this doctrine in an original way. Avicenna, in the eleventh century, maintained in his treatise on the soul that a particularly strong soul can act not only on its own body but also on external bodies, and gave the example of someone who falls from a narrow beam simply because he imagines falling.

Avicenna's theses, translated into Latin in the twelfth century, fuelled the debate of the schools for centuries. Thomas Aquinas and many theologians viewed them with suspicion, because they risked attributing to the human soul powers that belong only to God or the angels. Other authors, by contrast, found in them the key to explaining in natural terms phenomena considered prodigious.

Ficino, Pomponazzi and medicine

Marsilio Ficino attributed a decisive role to the imagination in the relationship between soul and spirit: images conceived intensely act upon the spirit, and through it upon the body. Pietro Pomponazzi, professor at Padua and Bologna, in De incantationibus, composed around 1520 and printed posthumously in 1556, tried to explain many supposed wonders without recourse to demons, attributing some of them precisely to the imagination and the confidence of those present.

The medicine of the time gave wide credit to these ideas. Very widespread, for instance, was the belief that a mother's imagination could imprint marks on the child in the womb, an idea that also leaned on the biblical episode of Jacob's rods in the Book of Genesis. These were baseless convictions, which modern science has abandoned.

Imagination in occult philosophy

Cornelius Agrippa devotes several chapters of the first book of De occulta philosophia to the imagination. He describes how the passions of the soul, born from the imagination, alter the body: fear makes one pale, anger inflames, desire transforms. He then reports, gathering them from ancient and medieval sources, stories of people believed to have been transformed by the intensity of thought, presenting them as cases handed down by the authors.

For Agrippa the human soul, when united with the world soul and animated by a strong desire, can extend its action beyond the limits of the body. This doctrine, which he shares with Avicenna, represents one of the boldest aspects of his philosophy and one of those that critics found most disturbing, because it seemed to reduce magic to the will of the practitioner.

Today the vis imaginativa belongs to the history of ideas, but the theme has not lost its interest. Renaissance reflection on the imagination anticipates questions that psychology and medicine continue to ask, with different methods, about the relationship between mind and body, and it shows how thin the boundary between natural philosophy and magic was.