What Ibn al-Haytham actually did, and why “father of the scientific method” overstates it
Every few weeks someone sends me a graphic declaring that Ibn al-Haytham invented the scientific method centuries before Bacon. I understand the impulse. The standard Western story did put the origins of experimental practice far too late. But the slogan replaces one myth with another, and I think the real achievement is more impressive when stated carefully.
What the evidence supports. In his Book of Optics (Kitāb al-Manāẓir), written in the early eleventh century, Ibn al-Haytham argued that vision happens by light coming into the eye from objects, against theories in which something goes out from the eye. More importantly for us, he tested optical claims with apparatus built for the purpose: tubes, screens, darkened chambers with apertures, arranged so that one condition could be varied while others were held fixed, and competing hypotheses checked against the results. In his Doubts concerning Ptolemy he criticised the greatest astronomical authority of his world for inconsistencies. That is a serious, systematic experimental practice centuries before the figures usually credited with starting it.
What the slogan adds that the evidence doesn't. There was no single “scientific method” for anyone to found, then or now. And he was not working alone: al-Biruni, his contemporary, was analysing measurement error with a care that deserves its own credit.
It's also not true that he is forgotten. UNESCO celebrated his optics during the International Year of Light in 2015.
I'd like to collect better ways of telling this story.