Weyer attributes all those famous transformations to imagination. That sufferers from hydrophobia seem constantly to see the image of a dog in their urine; that melancholy and sick people conceive so many fantastic visions and apparitions, entertaining such absurd images as that they are kings, lords, cocks, bears, apes or owls; that they are heavy, light, transparent, large or small, without sensation or dead, as will be shown more fully in our sections on symptoms: all this can be attributed only to a corrupted, false and violent imagination.

It works not only in sick and melancholy people, but sometimes with the greatest force in those who are healthy, suddenly making them ill and altering their constitution in an instant. Sometimes, too, a strong idea or impression will remove diseases, as Valesius demonstrates: in either direction it produces real effects. If people merely see someone else trembling, dizzy or sick with some fearful disease, their apprehension and fear are so strong that they develop that same disease.

Or if some soothsayer, wise man, fortune-teller or physician tells them they will have a particular disease, they take the prediction so much to heart that they immediately suffer from it. This is familiar in China, says Ricci the Jesuit: if people are told they will be ill on a certain day, when that day comes they will certainly be ill, and so terribly afflicted that they sometimes die of it.

Dr Cotta, in chapter 8 of his Discovery of Ignorant Practitioners of Medicine, has two strange stories showing what imagination can do. One concerns a parson’s wife in Northamptonshire in 1607. She went to a physician, who told her that he thought she was suffering from sciatica, a disease she did not have. That very night, after returning home, she suffered a severe attack of sciatica because of his words. He gives a similar example of another housewife troubled by cramp, which she acquired in the same way merely because her physician named it.

Sometimes the force of imagination causes death itself. I have heard of someone who happened to come into the company of a man thought to have the plague, although he did not, and suddenly fell down dead. Another fell ill with the plague through the mere thought of it. One person faints at the sight of his companion being bled. Another, Cardan says on Aristotle’s authority, fell down dead merely from seeing a man hanged—as commonly happens to women at any ghastly sight.

A Jewish man in France, says Luis Vives, happened to cross a dangerous passage, a plank laid over a brook, in the dark without coming to harm. The next day, realizing the danger he had been in, he fell down dead. Many will not believe such stories, but usually laugh and scoff when they hear them. Yet let them consider, as Peter Byarus illustrates the point, that if they were made to walk on a plank high above the ground, they would grow dizzy, though they would confidently walk on the same plank at ground level.

Many men otherwise stout-hearted, says Agrippa, tremble at such sights, become dizzy and feel sick merely from looking down from a high place. And what affects them except an idea in the mind? Just as some are troubled in this way by imagination, others are as easily restored by imagination alone and a favourable expectation.

We commonly see toothache, gout, epilepsy, the bite of a mad dog and many such ailments cured by spells, words, written symbols and charms; and many fresh wounds healed magnetically by that “weapon salve” now so widely used, which Crollius and Goclenius have recently defended in print, Libavius just as firmly opposes in a full treatise, and most people dispute.

Everyone knows that such charms or cures have no power beyond strong imagination and belief alone, which, as Pomponazzi maintains, set the humours, spirits and blood in motion and remove the cause of illness from the affected parts. We may say the same of magical effects, superstitious cures and those performed by quacks and wizards. Just as many people are harmed by wicked disbelief, says Weyer of charms, spells and the like, so we find from experience that many are relieved by the same means.

An empiric or a simple surgeon often performs more extraordinary cures than a learned physician. Nymannus gives the reason: the patient places his confidence in him, and Avicenna ranks that confidence above medical skill, rules and every remedy whatsoever. Belief alone, says Cardan, makes or ruins physicians; and according to Hippocrates, the one most trusted performs the best cures.

So variously does this imagination of ours affect, twist and turn, so imperiously command our bodies: like another Proteus or a chameleon, it can take every shape. Its power is so great, Ficino adds, that it can work upon others as well as ourselves. How else can sore eyes in one person cause the same complaint in another? Why does one person’s yawning make another yawn? Why does one man’s pissing often prompt a second to do the same? Why is a third disturbed by the scraping of wooden plates or the rasping of files?

Why does a corpse bleed when the murderer is brought before it, some weeks after the murder? Why do witches and old women cast the evil eye on children and bewitch them? It is because, as Weyer, Paracelsus, Cardan, Mizaldus, Valleriola, Cesare Vanini, Campanella and many philosophers think, one person’s forceful imagination moves and alters another’s spirits.

More than this: by such means they can not only cause and cure diseases, illnesses and various infirmities in people far away, as Avicenna supposes in On the Soul, book 4, section 4, but also move bodies from their places and cause thunder, lightning and storms, an opinion approved by al-Kindi, Paracelsus and some others. Thus I may confidently conclude that this strong conception or imagination is “the human being’s star,” and the rudder of this ship of ours. Reason should steer it, but, overpowered by imagination, cannot control it, and so allows itself and our whole vessel to be overruled and often overturned.

Read more about this in Weyer, On Witches, book 3, chapters 8, 9 and 10; Francisco Vallés, Medical Controversies, book 5, controversy 6; Marcello Donati, On Remarkable Medical Histories, book 2, chapter 1; Levinus Lemnius, On the Hidden Wonders of Nature, book 1, chapter 12; Cardan, On the Variety of Things, book 18; Cornelius Agrippa, Occult Philosophy, chapters 64 and 65; Camerarius, Leisure Hours, first hundred, chapter 54; Nymannus’s discourse On Imagination; Laurentius; and the man who “is worth all the rest,” Fienus, a famous physician of Antwerp who wrote three books On the Powers of Imagination.

I have digressed this far because imagination is the “conveying medium” of the passions: through it they work and often produce extraordinary effects. As imagination is more or less heightened or relaxed, and according to the disposition of the humours, so the passions act with greater or lesser force and make a deeper impression.