Galen is criticized for combining Plato's tripartition- cum -trilocation of the soul, in which each part constitutes its own source of motivation, with the demand that the faculty of voluntary motion is limited to the rational part, being the only one located in the brain and having access to the relevant nerves. While scholars have concentrated on small nerves as connective organs, this paper focuses on the pneuma , blood and innate heat. When the latter is increased, the irrational parts can affect the brain's function to such an extent that the rational part's volitions are reduced to their own desires.