Sinan ibn Thabit ibn Qurra was the son of Thabit ibn Qurra and the father of Ibrahim ibn Sinan. Although Sinan was extremely eminent in medicine his contributions to mathematics were somewhat less major but he still deserves a place in this archive as a contributor to mathematics in this remarkable family of scholars.
Thabit ibn Qurra, Sinan's father, was a member of the Sabian sect. The Sabian religious sect were star worshippers from Harran. Of course being worshipers of the stars meant that there was strong motivation for the study of astronomy and the sect produced many quality astronomers and mathematicians such as Thabit himself. Sinan was trained in medicine, a topic which his father had studied in Baghdad. His father's patron was the Caliph, al-Mu'tadid, one of the greatest of the 'Abbasid caliphs, and Sinan was brought up at the court where his father held the role of court astronomer.
Sinan's father Thabit died in 901 and the caliph al-Mu'tadid died the following year. Al-Mu'tadid had shown great skill in playing the various factions off against each other during his period of power but after his troops were defeated by the Qarmatians, a schismatic sect and political movement. Historians argue whether al-Mu'tadid was poisoned in a palace intrigue, but even if he was not this is an indication of the atmosphere in the court where Sinan lived. By this time Sinan was a man of about 22 years of age but, despite having great medical skills, he seems to have held no positions at this time.
On al-Mu'tadid death, his son al-Muktafi became caliph and succeeded in defeating the Qarmatian sect which had lead to his father's downfall. He ruled until 908 and Sinan certainly enjoyed a period of great cultural activity in Baghdad which was home to many intellectuals. However in 908 al-Muqtadir, who was only a boy at the time, became Caliph. He was a weak leader but his coming to power saw Sinan achieve his first major position in which he directed the hospitals and all medical activities in Baghdad.
Although the government in Baghdad slowly lost control, Sinan achieved the respect of all the factions. He was, as we mentioned at the beginning of the article, a Sabian and not a Muslim. However, he was totally fair in his treatment of people regardless of which religious group they belonged to and for this he gained respect. By 931 he had gained such authority in Baghdad that all doctors had to be tested by him before being allowed to practise.
Al-Muqtadir's reign ended in 932 and he was replaced by al-Qahir. Sinan faced a totally different type of regime, for al-Qahir persecuted the Sabians. Sinan tried to preserve his position by becoming Muslim but this was not sufficient to allow him to continue in Baghdad and he fled to Khurasan. The Abbasid caliphs were rapidly losing control and al-Qahir only survived for two years before ar-Radi became caliph in 934. This allowed Sinan to return to Baghdad but, in 935, the final political crisis occurred and ar-Radi was forced to hand over most of his power to the ambitious general ibn Ra'iq.
Ar-Radi died in 940 after a five year struggle to retain power and the problems only became worse as military leaders struggled for control. Sinan left Baghdad again to move this time to Wasit on the Tigris.
Despite his high profile medical career, Sinan seems not to have written any works on medicine. He wrote mainly on three topics, political history, mathematics and astronomy. However Sinan's political work in which he set out his ideas for a government modelled on Plato's Republic were criticised by the historian and traveller al-Mas'udi who known as the "Herodotus of the Arabs". Al-Mas'udi stated that Sinan should have :-
... occupied himself with topics within his competence, such as the science of Euclid, the Almagest Ⓣ, astronomy, the theories of meteorological phenomena, logic, metaphysics, and the philosophical systems of Socrates, Plato, and Aristotle.
No works which can definitely be attributed to Sinan have survived although it is claimed that he wrote four mathematical works, although in  the author points out that only two of the four could have beed written by Sinan, one on Archimedes work On triangles and one On the elements of geometry.
Article by: J J O'Connor and E F Robertson
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