Why Galen used dreams to diagnose patients

Galen (129 - 216 AD) relied on dreams as tools to help him diagnose patients, and he wrote about this practice in a text, called On Diagnosis from Dreams, that survives to us only in fragments.

The practice of using dreams as diagnostic tools originated at some point in the Classical Period of ancient Greece (508 - 322 BC). In an earlier post, I described the earliest medical text that explained the reliability of this practice. However, this practice even pre-dated that text because it was an important part of what we would call religious healing or what some scholars call temple medicine: healing cults thought that some dreams had been sent by the gods with information about what ails us.

Between the development of this practice and Galen’s time in the Roman Empire, a lot had changed when it came to this practice.

For starters, many thinkers had come to doubt that dreams could legitimately be used this way. Among this crowd, Soranus (1st - 2nd centuries AD) and Asclepiades (129 - 40 BC) featured most prominently.

Galen sharply disagreed, and he wrote On Diagnosis from Dreams to defend his position.

His history with dreams had started long before then, though.

When Galen was sixteen-years old, his father, Nikon, had vivid dreams that led him to send his son to study in Pergamum with a famous physician. In these dreams, Asclepius, a god of healing, commanded Nikon to ensure that Galen studied medicine in Pergamum.

When Galen was twenty-years old, he suffered from a subdiaphragmatic abscess. This was a nasty and rare condition in which bacteria has caused pus to accrue in the area between the diaphragm, liver, and spleen. In his book, Therapeutic Phlebotomy, Galen tells us that Asclepius told him to make a cut on his hand between the thumb and the first finger and let the cut bleed. Galen thought that this saved his life, and he says that this was the moment he became the god’s servant.

Dreams were an important part of his relationship with Asclepius. When he was thirty-eight-years old, he was commanded by Asclepius in a dream not to go to war. This meant not serving the emperor, Marcus Aurelius, but Galen thought that following Asclepius’ command was more important.

Lastly, five years after that episode, he received a dream-visit from another god who commanded him to finish his work on the optic nerve. In response, Galen accelerated his progress on that book.

Galen interpreted dreams as having real and practical significance for what we ought to do. This wasn’t just about him. In Outlines of Empiricism, he tells us this story about a patient:

“Another rich man, a foreigner from central Thrace, came to Pergamum as instructed by a dream. Then a dream came to him in which the god [Asclepius] ordered him to drink each day the drug made from wild figs, and to anoint the outside of his body. After a few days his condition became that of psoriasis, which, however, the god cured in turn by drugs that he prescribed” (Outlines of Empiricism 10).

These god-sent dreams were clearly very important to Galen, his worldview, and his medical practice. However, he didn’t think that all medical, diagnostic dreams were sent by the gods.

Galen believed that when we sleep, our soul turns inwards and investigates the interior of the body. It is then affected by substances in our body. These could be the humors, such as bile or phlegm, or other substances, such as semen. When we are awake, our soul is focused on external things, such as what we see or hear. But sleeping allows our soul to be a source of information about the interior of the body.

Here is what he says in a fragment from On Diagnosis from Dreams:

“The likely reason [for the occurrence of these dreams] is that after the soul has entered the interior of the body during sleep and has withdrawn from outside sense perceptions, it senses what the condition is through out the body, and it receives images of all the things that it desires, as if they were actually present” (K. 834).

This passage captures the idea I mentioned: dreams are produced when the soul withdraws into the body and senses what is going on.

What it interacts with determines the contents of the dreams. For instance, if there is a lot of semen, we have dreams of having sex. If there are a lot of humors, such as bile or phlegm, we dream of being weighed down by heavy burdens. If there is not, then we dream of being free and unencumbered.

Here is an example he gives:

“Likewise, a certain wrestler dreamt that he was standing in a cistern of blood and was scarcely able to keep his head above the level of blood. We took this dream as an indication of excess blood in his body and recommended that he undergo bleeding” (K. 834).

This one is interesting because it shows that Galen connects the dream-revealed diagnosis to a treatment (i.e., bloodletting to get rid of the excess blood).

None of this is simple or straightforward. Galen is emphatic that you have to pay attention to such details as what food the person ate, what time of the day did they have the dream, and so on. Not all dreams are indicative of something being wrong with us internally. Some, as we’ve said, are sent by the gods and might indicate something that they want us to do, such as finish a book. Some merely reflect what we did during the day.

Paying attention to these important contextual features can help us see where the dream originated and what it tells us.

Lastly, dreams were sadly often misinterpreted and misunderstood.

For example, Galen tells us the following story:

“Someone dreamt that one of his legs turned into stone. Now this dream was interpreted by many skilled in these matters as a reference to the man's slaves. However, contrary to all of our expectations, the dreamer became paralyzed in that leg.”

This is an important admission of a mistake in dream-interpretation. Galen does conceive of this as a science, but it is one that is open to the occasional error.

A similar story is told by Rufus of Ephesus (1st - 2nd century AD):

“Myron the Ephesian, who was a wrestler of seemingly good health, had the following dream. He dreamt that he spent the whole night in a black marsh of fresh water. When he woke up, he related this dream to his trainer. But the latter considered the dream to be of no account and put Myron to his exercises. When Myron was not even halfway through with them, shortness of breath and discomfort and palpitation throughout his chest set in. Then he had no control of his hands and feet, and shortly afterwards was unable to speak. Not much later he died. It seems to me that he would not have died if he had had a knowledgeable trainer and, instead of exercising, had effected for him a massive evacuation of blood.”

Sadly, this mistake was lethal, and Myron died due to the misunderstanding.

These stories illustrate the complexities surrounding diagnostic dreams. These complexities made the stakes higher for practitioners but ultimately did not discourage those such as Galen who were true believers in the practice.