In Thomas Aquinas’ commentary on Boethius’ De Trinitate, Thomas brings his favorite Aristotelian categories to bear on book reviewing.
While explaining Boethius’ preface, Thomas says that Boethius “sets forth… the four causes of his work.” Those four causes are the famous four causes from Aristotle’s Physics, where the philosopher declares that “we do not have knowledge of a thing until we know its causes.” Those four Aristotelian causes are
Material: What a thing is made of
Formal: How a thing is shaped or configured
Efficient: What work is exerted to bring a thing about
Final: The end or purpose for which a thing is designed
Boethius does not actually declare in his preface that he is going to enumerate the four causes of his book. Though he knew his Aristotle very well, he does not employ the terminology of fourfold causation here. It is Aquinas, in explaining Boethius, who brings out the Aristotelian vocabulary for its explanatory value.
If you’ve read much late medieval or early modern theology, you’ve seen a lot of this kind of thing. From Thomas Aquinas all the way down into some of the Protestant scholastics of the seventeenth century, the four causes are standard tools for making important theological distinctions: the four causes of Scripture, of justification, of merit, of you name it. When I read these authors and see them reaching into the conceptual toolbox for the four causes, I sometimes heave a little sigh because I know what’s coming. And sometimes it’s pretty tedious. But at their best, theologians from this time period use the four causes to bring real understanding or make very sharp distinctions indeed, and they apply them in unpredictable ways.
It never occurred to me to use the four causes for a book review. But Thomas Aquinas did it. What are the four causes of Boethius’ treatise on the Trinity?
First, the material cause: the subject matter is the doctrine of the Trinity, “the problem which,” Boethius says, “has been for so long a time the subject of my investigation.” No surprises there.
Second, the efficient cause Thomas breaks down into two sub-categories. The proximate or secondary efficient cause of the book is “the intellect of the author,” that is, the mind of Boethius which has done the work of causing the book. But when Boethius in his preface describes the book as coming from “the feeble spark of my mind” which “the divine light has caused to enkindle,” Thomas takes this as a clue that there is a greater, primary, and ultimate cause behind the spark of the author’s mind.