The Preserver and Unifier of the Temperament, Corresponding to the Principle of Substantial Motion – A Comparative Study of Khwāja Ṭūsī and Mullā Ṣadrā

One of the contentious topics in Islamic psychology (that deals with the philosophical study of the self) is the issue of the preserver and unifier of temperament. The human temperament is an accidental property that arises from the combination of opposing elements. Due to its diverse and opposing qualities, this temperament requires an agent to preserve it and prevent its disintegration. According to all Muslim philosophers, the human soul, after its creation, is the preserver and unifier of the body's temperament. However, the question arises as to who the preserver and unifier of the fetus's temperament is before the soul’s creation when there is no soul yet. Various answers have been provided to this question. Khwāja Naṣīr al-Dīn Ṭūsī has also addressed this issue in detail and ultimately provides an answer that is very close to the principle of substantial motion and the response of Mullā Ṣadrā. However, upon closer examination of this view, we realize that although Khwāja Naṣīr al-Dīn's answer approaches that of Mullā Ṣadrā’s principle and response, it cannot be claimed that Khwāja consciously or unconsciously resolved the issue based on the principle of substantial motion in alignment with Mullā Ṣadrā’s answer.