Such was its importance that the Isharat of Ibn Sina (d. 428/1037) was sarcastically described by Ibn Taymiyya as the ‘holy book (mushaf) of these philosophers’. It is a vital source for understanding the development of medieval Islamic philosophy, and because of its terse, almost oracular style, it is always studied with its commentaries - especially the hostile commentary by the great Ash‘ari thinker Fakhr al-Din al-Razi (d. 606/1209) and the defensive commentary by the Ismaili theologian and astronomer Nasir al-Din al-Tusi (d. 672/1274).
In the Fifth Namat of the Metaphysics of the Isharat, Ibn Sina discusses the impossibility of time having a beginning and also provides a definition of time. As Razi understands Ibn Sina’s argument, time cannot begin because every beginning which we posit for it has a ‘before’ which presupposes time.
Razi proceeds to attack this argument by trying to demonstrate that the parts of time, the ‘before’ and the ‘after’, are not real but nominal.
Tusi skilfully argues that these parts of time are neither real nor nominal but conceptual in status - they are internal sensa which point to a reality outside the mind, namely time. Moreover, in defending the claim against Razi that time cannot begin, Tusi finds a subtler argument in Ibn Sina’s text, according to which time is an absolute continuum and flux, such that its intrinsic identity would be violated if it were thought of as beginning.
Dr Toby Mayer is a Research Associate in the Qur’anic Studies Unit at The Institute of Ismaili Studies, London. After completing his undergraduate degree in Indian Studies at the University of Cambridge, he went on to study Medieval Arabic thought at the University of Oxford, where he wrote his doctoral thesis on the Book of Allusions (Isharat) by the major Persian philosopher Ibn Sina.