Gilson: Christian Philosophy of Saint Thomas Aquinas

From the 20th century’s leading Thomist.

Thesis: Only God is an ens per se, a being whose essence is its act-of-being.

Before we continue, we should probably get clear on Aquinas’s basic terminology:

Material substances are composed of matter and form.
Prime matter: possibility of being a substance (177).
Form: the act which constitutes substance.
Subject: once substance is constituted by the union of form with matter.
The relation of matter to form is the inverse of that of subjects and accidents.

The Plenum

Also known as “chain of being.” The best way to illustrate this is by Thomas’s doctrine of angels. Gilson notes that “the effects of the divine power are naturally ordered in a continuous series of decreasing perfection” (163). Indeed, “It is impossible to put immediately beneath God corporeal substance…A great number of middle terms must be posited by which we can descend from the sovereign simplicity of God to the complex multiplicity of material bodies.”


The human soul is an immaterial substance. It is also immortal. Gilson gives a nice critique of Plato: for Plato body and soul have only an external, contiguous contact (192). The soul controls the body like a motor.

Will and Act

Will is the soul’s higher appetitive power. It’s proper object is the general good (241). The will by definition cannot be constrained. God moves the will but this isn’t a necessity or constraint, for God moves it in conformity with its nature.

The Structure of the Human Act

Intention: the movement of the will which moves itself and all the other powers of the soul (252). This is a huge point concerning today’s discussions on philosophy of mind. Intentionality cannot be reduced to the merely physical. Therefore, naturalism is wrong. The will moves by seeing the intellect’s presenting to it universal being. A human act has two sub-acts that must be distinguished: the interior act of the will and the exterior act. Each act has its corresponding object (260).

Virtue: a habit which disposes us in a lasting way to perform good actions (259).

Social Acts

Gilson has an interesting take on social virtues, as seen in Thomas. But before we get there, we need to see what Thomas says by justice. This is key because “justice” is one of those words that some use to guilt-trip others out of their tax dollars. To be fair, Thomas is no libertarian, but he has thought through these issues better than most today.

Justice simply is equity of relations. Justice seeks the just mean in a relationship “between two things that are outside the virtuous man himself: his act, and the person whom his act concerns” (309). Justice seeks the mean of reason.

Aquinas’s take on justice cannot be abstracted from the aristocratic society in which he lived. Justice does not mean everyone gets the same. In means everyone is guaranteed the advantages due his rank (311). Aquinas also champions monarchy.

Gilson has a challenging section on usury. It is illicit to accept/give interest on a loan (325). Since money doesn’t breed money, you cannot sell what doesn’t exist.

I like what Thomas says, but it is clear that he didn’t imagine the commercial society we have today. Further, it isn’t the poor pauper who is getting burdened by usury. Rather, it is the industrious citizen who loans money to dissolute governments who will then debase the value with shady banking practices. How do we protect the businessman?


This isn’t my favorite book on Aquinas. Some sections were too long, yet not long enough. In other words, parts of Aquinas had to be skipped. That’s inevitable, but it is hard to do in a seamless fashion. On the other hand, Gilson is remarkably clear on what Aquinas means by being, substance, and essence. Further, the chapters on ethics were quite moving at tim

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