Circularity of the Definitions of Nature and Truth of Time in Ibn Sīnā’s View

Ibn Sīnā has provided two definitions for time, which Khwājah Naṣīr al-Dīn Ṭūsī believes to be circular. The first definition has appeared in Ibn Sīnā’s al-Ishārāt and introduces time as incompatible priority and posteriority. Some philosophers, such as Āqā Ḥussayn Khānsārī, believe that the circular nature of Ibn Sīnā’s definition of time in this book poses no problem because the concept of time is an axiom, and the existence of circularity in the definition of an axiom is natural. His other definition has been given in al-Shifā. Here, the nature of time is defined in the sense of a measure of motion as divided into prior and posterior components. In this definition, time contains disjunctive quantity (time as the number of motion) in addition to continuous quantity (time as amount of motion). The present paper aims to provide a clear picture of the definition of the nature of time in Ibn Sīnā’s view in his al-Ishārāt and al-Shifā in al-Ṭabi’iyyāt chapter. Following an analytic comparative study of Ibn Sīnā’s works, the author concludes that Khwājah Naṣīr al-Dīn Ṭūsī’s perception of Ibn Sīnā’s definitions of the nature of time were not inconsistent and, rather, he intended to provide another analysis of the truth of time.