ABSTRACT
For reasons internal to the evolution of their discipline, the mathematicians of the 9th century encountered the problem of the duality of order: is the order of exposition identical to the order of discovery? This question was very naturally first raised about the very model of mathematical composition at that time and for many centuries to come, namely, Euclid’s Elements. To this problem, Thābit ibn Qurra devotes a treatise in which he maintains that the order of exposition of the Elements is nothing but the logical order of the demonstrations and differs from the order of discovery. To characterise the latter, Thābit develops a ‘psycho-logical’ doctrine of mathematical discovery. In a sense, we are already on the terrain of the philosophy of mathematics.
