75 – In Question 75, Aquinas argues that the human soul is incorporeal because corporeal bodies are not the principle of life, else all bodies would be alive. We see that only bodies imbued with an incorporeal soul have life. This argument presupposes that a certain arrangement of well-functioning physical bodies cannot animate a body.
76 – In Question 76, Aquinas discusses the union of the body and soul. He argues that the soul is united to the body as the body’s form. The term “form,” as Aquinas uses it, means that by which a thing is actuated. Thus, the body is actuated by its form – the soul.
78 – In Question 78, Aquinas outlines the powers of the soul. He quotes Aristotle: “The powers are the vegetative, the sensitive, the appetitive, the locomotion, and the intellectual.”
79 – In Question 79, Aquinas discusses the intellectual powers of the soul. He argues that memory, reason, and morality are all powers of the soul.