Empirical findings of contemporary neuroscience suggest that human behaviour is entirely caused by neurobiological mechanism. In this way our common sense view of freedom and responsibility seems illusive. Searching for a philosophy of psychiatry, the author surveys contemporary theories of the ‘Philosophy of Mind’ (i.e. compatibilism, Non-Reductive Physicalism). Careful analysis reveals that they cannot consistently account for human beings as both neurobiologically determined and free. The author shows that for such an account the philosophy of Duns Scotus, an outstanding medieval thinker, offers some decisive conceptual clues. Thus, the outlines of a philosophy of psychiatry can be drawn, using the concepts of freedom and disposition. The combination of Scotism and psychiatry is also explored on a practical level by probing into a vital issue concerning faith and depressive disorders: man’s natural desire for God.