In Question 79 of Summa Theologica, Thomas Aquinas revisits Aristotle’s conception of the soul in order to encompass the intellectual capacity. In this paper, I will examine closely the Third Article in order to evaluate Aquinas’ argument supporting the existence of an active intellectual principle, which he denominates as the agent intellect.
Aquinas’ main hypothesis is that the intellect, which is a power of the soul, is divided into a passive and an active component. In the previous article, he skillfully proved that the passive component exists after broadly defining passive as that which passes from potentiality to act (Aquinas, 122). He then concludes that to understand is "in a way passive" (Aquinas, 123) since when we are born we are only in potentiality towards understanding, but later on, the potentiality becomes realized. Finally, active is implicitly defined as that which remains in potentiality.
The first argument against the existence of the agent intellect states that since the intellect is in potentiality to intelligible things, and since that potentiality becomes act through understanding, there is only a passive intellect. The next objection suggests that if the active component of sensory perception aids in making the medium luminous, then analogously, the active component of the intellect should also influence the medium to make understanding possible. However, since there is no apparent medium required for understanding to occur, there is no need for an agent intellect to alter the medium. The final objection states that since forms are allegedly immaterial, once they are received by the intellect, no further effort is needed by an active component to make them intelligible.
Aquinas answers these objections by reviewing the definition of a form. For Plato, forms are immaterial and completely independent of matter. However, Aristotle reviewed this theory by establishing a connection between matter and form which is based on the concepts of actuality and potentiality (Aristotle, 412a). Therefore, some power is required to break this connection and extract the form from individual matter. He calls this power to abstract the agent intellect (Aquinas, 128).
Aquinas methodically replies to the objections by using alluding to the definition of the intellect and its components. He answers the first objection by affirming that since the intellect needs to perform two actions, namely abstraction and understanding, there needs to be an active constituent to the intellect as well as a passive one, unlike the nutritive and sensitive parts of the soul. Aquinas responds to the second objection by clarifying Aristotle’s analogy of the active intellect as light: for the Philosopher, light is needed so that the medium becomes illuminated, but the agent intellect is required for understanding for a different reason since no medium is involved. The final objection is resolved by asserting that in order to comprehend the intelligible, abstraction is required to extract the form from the matter, a function performed by the agent intellect.
Aquinas line of reasoning has a very strong foundation to support it. Not only does it follow Aristotle’s carefully crafter arguments, but it also supports the modern conception of how understanding is achieved. By dividing the intellect, Aquinas defines very precisely the correlation between form and matter, which results in a very powerful tool to prove the existence of the agent intellect, as well as making the Theory of Forms more tangible. Finally, by responding to objections that might be presented to his ideas, Aquinas tackles alternative explanations before the reader even thinks of them, making the argument stronger and reinforcing the groundwork in the philosophy of mind.
Aquinas, Thomas. On Human Nature. Ed. Hibbs, Thomas. Indianapolis, IN: Hackett Publishing Co., 1999. 120-130.
Aristotle. De anima Trans. R.D. Hicks. Amherst, NY: Prometheus Books, 1999. 9-72