Final answer:
The soul, according to Aristotle, is not a substance of matter but rather the form of a living body, with actuality being the most accurate description. Each type of soul corresponds to a level of life function, with the human soul uniquely capable of reasoning.
Step-by-step explanation:
The soul is not a substance in the sense of potency/matter nor privation, and the composite of act and potency/form and matter is incorrect. For Aristotle, the soul is the form of the living body, equated with actuality. In his works, including 'On the Soul' and 'Generation of Animals,' he describes different types of souls that correspond with various forms of life, such as vegetative, animal, and human, with the human soul possessing the unique capability to reason. This capacity for rational thought sets apart the human soul from those of plants and non-human animals, as it gives humans the first principle of life and aligns with the essence or substance of a human being.
According to Aristotle's functional understanding, the soul is intrinsic to life itself, with the vegetative soul promoting growth in plants, the animal soul allowing for perception and movement, and the human soul adding the power of reason. This indicates that the soul's essence is its functional activity within the living body, which cannot be considered corporeal but rather as the formal cause or shaping principle of a living being.