Untangling Determinism: Revisiting the Principle of Sufficient Reason in the Post-Avicennian Debates on Free Will


Avicenna was one of the premodern philosophers who argued for the Principle of Sufficient Reason (PSR), namely the claim that everything has a cause and that no uncaused beings can exist. One of the consequences of PSR is necessitarianism, which is the assertion that whatever exists actually also exists necessarily because each and every member of the causal chain is determined by antecedent causes. PSR thus goes against human intuition that suggests that things could have been otherwise. My goal is to investigate whether post-Avicennian authors tried to mitigate the necessitarian consequences of PSR by excluding human will from it. I will concentrate on the comparison between Naṣīr al-Dīn al-Tūsī’s (d. 1274) Persian treatise Jabr va qadar and his theological summa Tajrīd al-iʿtiqād. The immediate reason for choosing this issue is al-Tūsī’s assertions that humans intuitively know that they are autonomous agents of their actions, which seems to contradict the universal applicability of PSR. I will argue that al-Tūsī espoused somewhat different views on free will. Depending on the character of the texts and the period in which they were written, sometimes being consistent with Avicenna while other times engaging with Muʿtazilism. I will show how al-Tūsī left room for human freedom, however causally ineffective at times, which he understood as a different kind of determination that is able to act independently of the other types of determination to which humans are subject, be they physical or divine. Overall, the discussion tests al-Tūsī’s allegiance to either Avicennian philosophy or Shiʿi theology and even forces him to take a stance against Avicenna’s view on knowledge in some of his works.


necessitarianism free will PSR determinism indeterminism Nasīr al-Dīn al-Tūsī