Hasan Ibn al-Haytham and the Scientific Method

Take a guess as to what this Medieval illustration is a drawing of: upside-down fallopian tubes? Sea-creatures? Mirror-image diagrams of some planetary motion? The answer is below, but before you look — ask yourself how you are arriving at your guesses.

The process of investigative inquiry to figure out the nature of reality is something we tend not to think about, but most of us learned back in our early schooling that it involves the scientific method. And we’ll remember that entails observation, hypothesis, testing through experiments, and repeatedly verifying the conclusions. But this process didn’t used to be the norm — until an intellectual named Hasan Ibn al-Haytham (c. 965-c. 1040) recorded his methodology, which was later repeated by increasingly larger numbers of scientists until it was universally accepted.

Before al-Haytham, in Europe and the Middle East, deductive logic and reliance upon established authorities were considered the best ways to get answers to Life’s Big Questions. But that way of course leads to confirmation bias and a lack of new intelligence. Al-Haytham taught that truth-seekers instead need to approach their assumptions with skepticism, writing that:.

“If learning the truth is (a man’s) goal,” he should “make himself an enemy of all that he reads, and . . . attack it from every side . . . He should also suspect himself as he performs his critical examination of it, so that he may avoid falling into either prejudice or leniency”.

This methodology al-Haytham outlined in his best-known work, _Kitāb al-Manāzir_, _The Book of Optics_. In it, he carefully detailed the experiments that allowed him to determine important features about how eyes work, like the fact that they see because light reflects from objects into eyes, rather than being created by light going out of eyes (like teensy flashlights, which is what Aristotle et al. had thought).

The image here is from a later manuscript of al-Haytham’s, showing the anatomy of an eyeball.

Fun fact about al-Haytham: he was hired by an unstable Caliph of Egypt to do consultation work on how to best manage the Nile River. But al-Haytham knew the Caliph’s temperament (the ruler had at various times forbidden women to leave their homes, commanded all dogs be slaughtered, and that everyone work outside at night and sleep during the day. He also ordered many assassinations.) Realizing his advice was going to make the Caliph upset, al-Haytham faked being insane and was put under house arrest for ten years. This worked great for the scientist — he got both his life and time to study and write. After a decade the Caliph was assassinated and al-Haytham became a teacher.