Within the depth-psychology corpus, Reason occupies a contested and multivalent position: simultaneously the highest faculty of the rational soul, a cosmological principle identical with divine law, a faculty whose sovereignty is perpetually threatened by passion and necessity, and—in the modern neuropsychological literature—an instrument whose very reliability is called into question by the hemisphere that wields it most confidently. The Stoic tradition, represented here through Inwood and Sorabji, identifies Reason with the immanent logos of Zeus, the normative standard against which every impulse is measured and to which the sage freely submits. Chrysippus insists that the human being is by nature constituted to follow Reason in every situation, yet passion arises precisely when a violent counter-motion overrides that commitment. Plato’s Timaeus, via Cornford, introduces the complementary tension between Reason as purposive cosmic design and Necessity as an irreducible irrational residue that Reason can persuade but never wholly eliminate. Aristotle, through Lorenz, treats Reason as that which can progressively civilize the non-rational parts of the soul, though appetite and spirit each relate to it differently. John of Damascus systematizes the soul’s faculties into those that obey Reason and those that do not, grounding moral anthropology in this structural distinction. McGilchrist, finally, subjects the entire tradition to hemispheric critique: the left hemisphere’s mode of rationality is itself only a partial and retrospective representation of the full living process of reasoning, which exceeds any post-hoc logical reconstruction.