Did Ibn al-Haytham, the man who explained vision, invent the scientific method?

It depends whom you ask: some call him the world's first true scientist, others see a gifted experimenter working inside a long tradition. Ibn al-Haytham, known in Latin as Alhazen, wrote the seven-volume Book of Optics between 1011 and 1021, and in it he tested ideas about light instead of just repeating them. Before him, two theories of vision competed. In one, the eye sends out rays; in the other, forms travel into the eye from objects. Alhazen built a theory that combined Euclid's mathematical rays, Galen's medicine and Aristotle's idea of something entering the eye. He also showed through experiment that light travels in straight lines, and he varied the aperture size, the focal length and the light source in his studies of the camera obscura.

That is why he is sometimes described as the world's "first true scientist": his admirers see him as an early proponent of the idea that a hypothesis must be supported by experiments based on confirmable procedures or mathematical reasoning, five centuries before Renaissance scientists.

Others are more cautious. G. J. Toomer warned that passages can be read anachronistically and that Alhazen should not be considered in isolation from other Islamic and ancient thinkers. Craig Aaen-Stockdale notes how close his account of vision stays to Ptolemy's: Alhazen corrected him on binocular vision, but otherwise his account is very similar.

His own words show the attitude. The seeker after truth, he wrote, is not one who trusts the ancients, but the one who suspects his faith in them and questions what he gathers from them. Legend adds a story: that he feigned madness and lived under house arrest in Cairo, where he wrote the Book of Optics.