Review: “Aquinas’ Proofs for God’s Existence” by Dennis Bonnette

In Aquinas’ Proofs for God’s Existence: St. Thomas Aquinas on: “The Per Accidens Necessarily Implies the Per Se Dennis Bonnette investigates the legitimacy of Aquinas’ principle (the per accidens necessarily implies the per se) and how it functions in Aquinas’ proofs for God’s existence. In particular, Bonnette examines how it is the key to the solution to the problem of infinite regress.

In Part 1 of the book Bonnette takes it upon himself to show that the principle is true in a number of contexts.

In chapter 1 he explains why if you have an accident (the per accidens) you must have a substance (the per se).

In chapter 2 he examines change. He notes that, in the context of a change, the preceding form (the per accidens) requires a succeeding form (the per se). He also notes that something must exist one way before the change and one way after the change. This something is matter in the case of accidental change and prime matter in the case of substantial change. Matter or prime matter is the per se principle in change.

Chapter 3 covers knowledge. Bonnette begins by explaining why a per accidens sensible object requires a per se sensible object. He then looks at intellectual knowledge and the three acts of the mind (apprehension of forms, judgment, logic). He explains why per accidens forms can only be understood in relation to being (the per se), why per accidens judgments rely on the principle of non-contradiction (the per se), and why per accidens propositions can only be known through the logical analysis of per se propositions.

Part 2 of the book examines how the principle the per accidens necessarily implies the per se functions in Aquinas’ proofs for God’s existence. This part has its own introduction and the chapter numbers start over at one.

The introduction looks at existence in an absolute sense. Anything that is brought into existence by an efficient cause has per accidens existence. Only the First Cause, God, has per se existence.

Chapter 1 looks at an argument for God’s existence given by Aquinas in De Ente et Essentia 4. Bonnette tells us why Aquinas believed essence and existence are distinct since this belief underpins  Aquinas’ argument. Things with per accidens existence are a composite of essence and existence. Aquinas argues that the First Cause of such things must be something whose essence is existence. In other words, per accidens existence depends on God’s per se existence.

Chapter 2 contains general comments about the Five Ways. Bonnette explains that Aquinas’ objection to an infinite regress is based on his understanding of proper causality (as opposed to accidental causality) and not on the impossibility of an actual infinite. A proper cause operates simultaneously with its effect. When a proper cause ceases, the effect also ceases. An infinite regress of proper causes is what Aquinas holds to be impossible. This denial of an infinite regress of proper causes is used in the Five Ways.

Chapter 3 examines the principle in relation to the First Way. The existence of moved movers (the per accidens) requires the existence of an Unmoved Mover (the per se). In the final section of the chapter Bonnette responds to contemporary commentary. In particular, he argues that Aquinas is speaking of proper causality and not causality back through the past. This includes a comment about proper causality in relation to the law of inertia.

Chapter 4 examines the principle in relation to the Second Way. The existence of dependent efficient causes (the per accidens) requires the existence of an independent efficient cause (the per se).

Chapter 5 examines the principle in relation to the Third Way. The existence of contingent entities (the per accidens) requires the existence of a necessary entity (the per se).

Chapter 6 examines the principle in relation to the Fourth Way. The gradation of being and its transcendental modes (the per accidens) requires the existence of absolute being (the per se).

Chapter 7 examines the principle in relation to the Fifth Way. The existence of orderly activity by mindless entities (the per accidens) requires the existence of an intelligent cause that orders those activities (the per se). This chapter contains a good discussion of how the term “chance” is used by Aquinas in this argument and why it can’t be an explanation for the orderly activity of mindless things. Bonnette also argues that an infinite regress of final causes is impossible.

The conclusion notes that each of the Five Ways employs efficient causality in leading one from some per accidens point of departure back to a first uncaused cause which is per se. Since Aquinas himself did not provide a full defense of the principle, here Bonnette provides a defense of its universality to tie the book together.

I consider myself a beginner in understanding Thomism. You should have some understanding of Thomism (at least its metaphysics and natural theology) before reading this book. It provides a solid discussion of the per accidens, the per se, proper causality, and the Five Ways. The book is not intended to prove all of Aquinas’ views, but rather builds off of them in elucidating the principle and the Five Ways. This means the book does not set out to prove God’s existence from scratch. What it does do is provide important commentary on the Five Ways to help the reader better understand the arguments.

Based purely on content, I recommend the book (if its subject sounds interesting to you). But, at the time of this writing, the book is priced at about $120. I can’t tell you that you will find its contents this valuable. You will have to use your own discretion.


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