The definition of the soul as a principle of Psychology according to Thomas Aquinas

In this article we want to show the rigorous and enlightening contribution that saint Thomas Aquinas makes to the relationship between the two definitions of soul presented by the Stagirite in De anima. At the beginning of Book II of that work, Aristotle gives two definitions of the soul that stand with each other in a demonstrative relationship. Aquinas' commentary on said passage explains this demonstration keeping in mind Aristotelian epistemology and physics, allowing a scientific understanding of that key piece that is the definition of soul, since the definition and essence of the subject is the principle of science.