Aquinas's Way to God
The Proof in De Ente et Essentia
The question of whether God exists is fundamentally philosophical in that whether or not God exists will have an impact on the interpretation of each and every feature of reality in a way the existence of no other entity could have. Recent discussions in philosophy and theology however, often seem ignorant of the importance of this question, or assume that it can only be answered in the negative. On the one hand, continental theology often appears happy to join forces with postmodernism in no longer treating the existence of God as an intelligible topic of reflection. On the other, many philosophers today seem convinced of a naturalistic atheism and assume that it has been shown that God does not exist.
Gaven Kerr’s Aquinas’s Way to God. The Proof in De Ente et Essentia provides a powerful argument against postmodernism and naturalistic atheism by analysing and justifying what could be referred to as Aquinas’s “metaphysical proof” (xii) for the existence of God. Kerr’s analysis of Thomas’s argument can be stated as a logically valid argument as follows: (1) If there are multiple entities, then there is a real distinction between esse and essence. (2) If there is a real distinction between esse and essence, then there is a being whose essence is its esse. (3) There are multiple entities. Therefore: (4) There is a being whose essence is its esse. (5) This being is what we call “God”.
To show that this argument is sound it must be shown that the premises are true. Kerr first clarifies the concepts of esse and essence: “Esse/existence for Aquinas is a real principle of act of a finite existent irreducible to anything more fundamental, such that the thing would not exist unless it has such a principle and without it there would be nothing simpliciter” (8). In contrast to esse, “essence for Aquinas is the principle by means of which a concrete thing is the type of thing that it is and no other” (38).
Based on these concepts, Kerr shows that the first premise of the argument for the existence of God is true: If there are multiple entities, then there is a real distinction between esse and essence. The reason for the truth of this premise is that, from a conceptual point of view, a being whose essence is identical with its esse cannot admit of any kind of multiplicity given that multiplicity presupposes that the essence of some entity can be specified in a formal or material way—which is precisely excluded for that being whose essence is plainly to be. Therefore, if there was no real distinction between esse and essence, then there could not be multiple entities. In other words, if there are multiple entities, then there is a real distinction between esse and essence: “If it is granted that there are multiple entities, then such entities, whatever they may be, will be subject to essence/esse distinction; for whatever such entities may be, qua multiple they are not that being whose essence is its esse, because that being can only be one” (29).
In a second step, Kerr justifies the second premise: If there is a real distinction between esse and essence, then there is a being whose essence is its esse. To show the truth of this premise, Kerr first justifies Aquinas’s causal principle: “If something—(x)—possesses some property, F, then x possesses F either as a result of the principles of its own intrinsic nature, its x-ness, or as a result of some extrinsic principle(s), y” (97). Based on Aquinas, Kerr then goes on to argue that no esse-essence composite possesses esse because of its own intrinsic nature and that, therefore, the esse of esse-essence composites is caused by some extrinsic principle.
Now, either this extrinsic principle is another esse-essence composite or it is that whose essence is its esse. In the first case, because for each esse-essence composite its esse is caused by an external principle, there is an infinite chain of causes in which the esse of a particular esse-essence composite is always caused by another esse-essence composite. In the second case, there is a finite chain of causes and that whose essence is its esse is the primary cause of esse in esse-essence composites.
To exclude the first option, Kerr emphasizes that, “in an infinite series of causes there is no primary cause, because if there were, it would ipso facto be a finite series” (141). He then argues that regarding the causing of esse in esse-essence composites “one cannot remove any of the prior causes of the particular series and yet hope to sustain the effect” (138-139). If A causes the esse of B, then without A, B ceases to exist. Based on this assumption, however, it follows that if the chain of causes of esse was an infinite chain in which the esse of a particular esse-essence composite is always caused by another esse-essence composite, then–considering each member of this causal chain has its esse from another member–the causal chain itself could not exist. There would be nothing, so to speak, that pours esse into this chain of causes in the first place: “To deny the primary cause … (i.e. to affirm the possibility of an infinite such series), is precisely to remove the causal efficacy of the causes within the series, which is in effect to deny the causal series itself” (142).
Therefore, since the chain of causes of esse cannot be infinite, it follows that the extrinsic cause of the esse of esse-essence composites can only be that whose essence is its esse: If there is a real distinction between esse and essence, then there is a being whose essence is its esse. Futhermore, according to Kerr, the third premise–There are multiple entities–is obviously true, it follows that there is something whose essence is its esse. This, however, is what we call “God.”
Kerr’s book is quite excellent and recommendable to all those interested in current debates about the existence of God, and God’s relation to the world. Not only does he propose a coherent and consistent interpretation of the proof for the existence of God in Thomas’s De Ente et Essentia, Kerr also shows that current philosophical discussion has little to offer to refute the argument and its presuppositions. We need more theology like this.
Benedikt Paul Göcke is on the faculty of theology and religion at the Ian Ramsey Centre for Science and Religion at the University of Oxford.
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