Psychiatrists can’t agree on how to define—let alone treat—even the most common mental disorders. Maybe examples from antiquity can help. After all, the way we think about mental illness might change almost constantly, but the issues we deal with never really do. William Harris, a professor of history at Columbia University, recently edited a volume of essays, Mental Disorders in the Classical World, covering topics ranging from the early Greek medical vocabulary of insanity to Rufus of Ephesus’ epistemology of melancholy. Harris’ contribution focuses on concepts of hallucination in ancient Greece and Rome.

Alice Robb: What did the Greeks and Romans hallucinate about?

William Harris: They did not have a single concept of "hallucination" until very late on, but they left us quite a number of vivid descriptions of both auditory and visual hallucinations. The most famous are probably the visions of the Furies suffered by Orestes after he murdered his mother, and the "voice" that gave advice to Socrates. In my opinion, the story of the resurrection of Jesus is based on a hallucination, probably by Mary Magdalen.

They mostly hallucinated about divine figures of one kind or another, but sometimes also human scenes such as the one Galen describes in which a certain Theophilus thought that flute-players were playing in his house all day and all night.

AR: How did they understand hallucinations? What did they attribute them to?

WH: For most people, I think, the gods were responsible one way or another, but for quite a number of others the causation was medical (no clear theory emerged of how that worked), while still others (the Epicureans in particular) adopted a naturalistic view on philosophical grounds.

The Epicureans were strict materialists, and they thought that images in the mind were caused by atoms flying through the air, there being huge numbers of these at any given moment. The mind always wants to make such images into intelligible shapes but sometimes it makes mistakes, especially when the person is tired—hence hallucinations.

AR: Did they see hallucinations as a problem—did they “treat” them?

WH: Yes, sometimes, and this was not just what doctors wanted. In Plautus' play The Menaechmi, for example, when a character "hears" the voice of Apollo telling him to commit a murder, the other characters in the play assume he needs a doctor.

AR: Do you think we over-medicalize hallucinations today?

WH: That's a hard one: On the one hand, many, many hallucinations are essentially harmless (in some cultures more than others), and it seems dangerous to treat them as symptoms of schizophrenia; on the other hand, some people are seriously bothered by their hallucinations. On balance, my answer is yes—but I am not a psychiatrist.

AR: Why should we look at concepts of mental disorders in the classical world?

WH: Since the Greeks invented rational medicine and their medical ideas remained dominant in the West until the 18th century, those ideas are a significant part of our own history. They included lengthy reflections about mental disorders, which also received close attention from some of the greatest literary figures of classical antiquity, including Homer, Aeschylus, Sophocles, Herodotus, Euripides, and Plato.

We also, ourselves, need all the help we can get in thinking about mental disorders: Witness the controversies that have surrounded all five editions of the Diagnostic and Statistical Manual of Mental Disorders, including the most recent one (2013). I agree with those scientists who think that our categories of mental disorders need a further shake-up.