The problem of predestination and free will is one of the very old and controversial issues with many doubts hovering over it, but the late Muḥaqiq Nāʾīnī, seeking the help of revelation (i.e. the Qurʿan), was able to dispel all of them with one answer which he termed as "the divine secret that God gave him."
In this article, the late Nāʾīnī's theory about free will, which consists of paying attention to the reality of action and the use of power, is explained, and corroborated by rational reasoning and evidences from verses and narrations. The theory of philosophical determinism, which interprets existence in the form of evolution and passivity, is explained and examined, and it is proved that, contrary to the view of philosophers, causality has three types: creation, action, and evolution. The result of the exclusive interpretation of causality to evolution is not confined to philosophical determinism, rather it leads to the theory of the realization of the universe without a creator, and as a result, the law of causality is simply ignored.