  In order to explain how animate beings perform different functions and operations, traditional psychological as well as physiological theories referred to a threefold soul. Whereas Aristotle in De anima had distinguished between the anima vegetativa, anima sensitiva and anima cogitativa (which distinction also corresponds to that of plants, animals and humans with their specific faculties), Plato had established three parts of the soul (Republic 434d-443e), which in the Timaios (69aff.) he had associated with different organs, namely the rational part of the soul (logistikon) to the brain, the spirited (thumoeides) to the heart and the desirous or lower passions (épithumêtikon) to the liver. In this tripartition he was followed by the Stoic physician Galen (De placitis Hippocratis et Platonis VII, I and III), who added a threefold spirit—the spiritus naturalis being produced in the liver, the spiritus vitalis refined in the blood and the spiritus animalis distilled in the brain. Whereas the Aristotelian psychology was combatted in the De rerum natura, Telesio dedicated a whole treatise to the criticism of Galen, the Quod animal universum ab unica animae substantia gubernatur. Contra Galenum. According to Telesio, the functioning of an organic body cannot be explained by presupposing a plurality of rulers. In asserting the unity of the soul (i.e. spirit), Telesio followed the medical theorist Giovanni Argenterio (1513–1572), who defended the unity of the spirit against the Aristotelian and medical traditions.