Although the main focus of this book is on Aquinas's proof of God's existence in the De Ente et Essentia, Kerr gives a thorough‐going account of Aquinas's metaphysical thought and he shows how a serious engagement with contemporary philosophy can help one to gain a deeper understanding of what Aquinas is saying.
The book is split into two parts. The first part is on the essence‐esse distinction and the second part is on the proof of God's existence. To begin with, Kerr discusses the controversy over how the first two stages of the proof of the essence‐esse distinction should be interpreted. Stage one is where Aquinas gives the example of a man and a phoenix showing that we can understand the essence of something without knowing anything of its esse. Stage two is where Aquinas argues that there can be at most one thing whose essence is its esse. One of the main issues at stake is whether Aquinas in the first stage establishes a real distinction between essence and esse or whether he only establishes a conceptual distinction. Kerr is not afraid to nail his colours to the mast and side with Wippel's interpretation that Aquinas only establishes a conceptual distinction in the first stage. Following Wippel, Kerr believes the second stage is a modal form of argumentation; that is, by establishing that it is conceptually impossible for there to be more than one thing whose essence is its esse, it must follow that it is actually impossible for this to be the case.
Not everyone is going to be convinced by this argument thus interpreted. My worry is that if one speaks of a being whose essence is its esse without presupposing that our two intellectual operations of simple apprehension and judgment correspond to a real distinction in things, then our concept of such a being might be indistinguishable from our concept of esse commune and that all that has been established in the second stage of the argument is that it is impossible for there to be more than one concept of esse commune. This is obviously not what Aquinas was trying to prove. Still, it is to Kerr's credit that he clearly acknowledges the various different interpretations of Aquinas's argument and he also provides a comprehensive list of sources so that the interested reader can undertake further investigation if so desired.
Having analysed Aquinas's proof of the essence‐esse distinction, Kerr goes on to give a more detailed account of Thomistic essentialism and he compares it with contemporary versions of essentialism which have emerged out of developments in quantified modal logic. This is just the kind of philosophical engagement any modern Thomist should be undertaking, and Kerr illustrates well how this can be done. Without getting too bogged down with the technical details, Kerr clearly shows how the contemporary approach differs from the Thomistic one and he presents some of the key challenges a Thomist could make to the contemporary essentialist.
Kerr then gives a similar treatment of esse, first presenting a detailed account of Thomistic esse, and then comparing it with various contemporary accounts of existence. In laying down the contemporary existential landscape, Kerr begins with Meinong's account in which non‐existing objects are understood to enjoy some sort of very basic reality. Following this, Kerr considers four other accounts of existence which he characterises in terms of their relation to the Meinongian view. These are (i) the Frege‐Russell‐Quine account, (ii) Lewis's indexical possibilist account, (iii) Salmon's indexical actualist account and (iv) actualist accounts which reject non‐existing possibles but still hold that there is an important contrast between the actual world and possible worlds. As Kerr sees it, the main problem with these four accounts is that they attempt to interpret existence in terms of something more fundamental, but it is very helpful to have these accounts before us so that we can see how very different Aquinas's understanding of existence is. Kerr makes a good case for why a contemporary philosopher might want to take seriously Aquinas's interesting and alternative account.
In the second part of the book, Kerr proceeds to present Aquinas's proof of God's existence as pure esse. In analysing this proof, Kerr devotes a chapter to discussing the causal principle that the properties a thing possesses either result from the thing's essence or from an extrinsic principle. The following chapter is devoted to the role of infinite regress in Aquinas's proof as well as the per aliud principle, which is the principle that everything that exists through another is reduced to that which exists through itself as to its first cause. Again Kerr gives a good overview of the main hermeneutical issues as well as possible responses to objections. In particular, he gives a very helpful account of why one should reject infinite per se causal series.
With God's existence having been established, Kerr discusses the intelligibility of God as esse tantum and the compatibility of this understanding with christian tradition. He gives a robust response to Kenny's argument that it is impossible to make sense of esse tantum in a post‐Fregean climate, and he also explains why conceiving God as esse tantum is no barrier to conceiving of God as a person. Finally, Kerr ties everything together with a chapter on creation in which he articulates the radical nature of God's creative act, and why the speculation of physicists can never undermine this doctrine if one has a proper understanding of esse.
In a paper titled ‘What Future has Catholic Philosophy’, John Haldane claimed, perhaps somewhat controversially, that if St. Thomas were alive today, he would be an analytical philosopher. A rather less controversial claim would be the suggestion that if St. Thomas were alive today, he would have seriously engaged with what analytical philosophers are saying. On this count, Kerr's book is a highly commendable illustration of what modern‐day Thomism should look like.
