Muhammad Ibn Zakariya al-Razi, the famous physician and philosopher of the Islamic world, has been considered by many researchers in different aspects. His theory of perfection of the soul, however, is not much appreciated in recent scholarship. Without learning philosophy, he believes the soul cannot be perfected and released from the body after death. This proposition begs the question: What will be the fate of the soul after death if it is not sufficiently perfected? Reincarnation, responds al-Razi. His view on (...) reason and reincarnation sets forth a dilemma in his philosophy. The conception of reincarnation implies two propositions: only human beings are rational, and the transmigrated soul eventually returns to the human body, so that it once again tries to achieve perfection. These propositions raise two questions: Why is the soul rational in the human body and irrational in animals? If rationality is an accident for the souls, how does it survive death? This paper aims to provide a flawless solution for this dilemma through a critical analysis method. Before this, previous attempts for achieving such a solution must be investigated. Therese-Anne Druart has suggested that, for al-Razi, animals have reason to some extent. Therefore, the soul is rational, whether it is a human soul or that of animals. Contrarily, Peter Adamson argues that al-Razi has regarded animals as deprived of reason, although they can think. Providing six arguments, Adamson argues that al-Razi does not believe in reincarnation. This way, there will be no reincarnation in al-Razi’s philosophy to lead him to the dilemma. We propose that neither of the above solutions can solve the dilemma of reincarnation because al-Razi believes in both reincarnation and depriving animals completely of reason. He does not regard rationality as a condition for the survival of the soul after death. Al-Razi has been influenced by Plato and also mostly by Galen and is opposed to Aristotle’s view on the soul. So, his conception of the soul should be conceived in a Platonic sense, not an Aristotelian one. Accordingly, the soul is an eternal self-mover entity and rationality is not the criterion for the survival of the soul. Besides, al-Razi indicates that a human being’s reason is due to the particular temperance and structure of his body, especially the brain. Consequently, the soul does not need rationality to survive death. Moreover, the nature of the soul is not necessarily rational. Although the view of reincarnation faces many problems, as many Muslim philosophers have criticized it, this investigation can pave the way for further research on the nature of the soul from al-Razi’s viewpoint. (shrink)