A ninth-century Baghdad philosopher invented the codebreaker's favourite trick
Counting how often each letter appears in a secret message, then matching the commonest symbols to the commonest letters, is called frequency analysis. Al-Kindi described it in Baghdad more than a thousand years ago, in the earliest known use of statistical inference. He also wrote on swords, perfumes, tides and earthquakes.
Abu Yusuf Yaqub al-Kindi, known in Latin as Alkindus, lived from about 801 to 873. He came from an aristocratic Kufa family of the Kinda tribe; his father governed Basra, where the boy had his first schooling. In Baghdad the caliph al-Ma'mun placed him in the House of Wisdom, the new centre for rendering Greek science and philosophy into Arabic, and successive caliphs put him in charge of translation work. He was prized for his calligraphy as well.
Contact with the ancients' philosophy turned him into its great Arabic champion. He wanted to show that Aristotelian and especially Neoplatonic ideas could sit comfortably alongside Islamic theology, though he held revelation to be the higher source of truth. Later thinkers found his prose clumsy, partly because nobody had written philosophy in Arabic before him, yet much of the standard Arabic philosophical vocabulary started with him, and figures such as al-Farabi, Avicenna and al-Ghazali built on that groundwork.
His range was startling. Alongside al-Khwarizmi he helped bring Hindu numerals into Islamic mathematics. In medicine, where he followed Galen, his De Gradibus proposed a mathematical scale for a drug's strength, which the historian Plinio Prioreschi called the first serious attempt to quantify medicine. In optics he weighed Aristotle's theory of vision against Euclid's straight-line rays and preferred Euclid, because only geometry explained why a circle seen edge-on looks like a line. Roger Bacon rated him second only to Ptolemy on the subject.
Fortune turned under later caliphs. Under al-Mutawakkil he was beaten and his library temporarily seized, whether because of rivalries at the House of Wisdom or the caliph's persecution of unorthodox thinkers is unclear, and Henry Corbin describes him dying lonely in 873. Ibn al-Nadim credited him with at least 260 books, most of which vanished; some survived in Gerard of Cremona's Latin versions, and 24 lost works turned up in a Turkish library in the mid-twentieth century.
Source: Al-Kindi
