Book Reviews, Christian Doctrines, Divine Simplicity, philosophy, Thomistic Philosophy

Book Review: “On a Complex Theory of a Simple God” By Christopher Hughes

Christopher Hughes’ work, On a Complex Theory of a Simple God: An Investigation in Aquinas’ Philosophical Theology (hereafter CTSG), is part of a series of books (on independent topics by different authors—meaning one can jump in on whichever book one wants) called the “Cornell Studies in the Philosophy of Religion.” It is the first book in the series which I have read (though I have 5 more sitting on my shelf), but if it is any indicator of things to come, I highly recommend this series.

CTSG mostly focuses on Thomistic Philosophy, but it specifically highlights St. Thomas Aquinas’ arguments for Divine Simplicity and his discussions of the Trinity and the Incarnation. I must admit that initially I found it hard to maintain interest in this work. Thomistic Philosophy is by no means a specialty of mine, and I got the book mostly because I was vaguely interested in whether or not Divine Simplicity—that is, the idea that God is “omnino simplex”, altogether simple, and “in no way composite” (Hughes, 4). Hughes, however, manages to make a topic in which I displayed only a passing interest into a page-turner of a philosophical work.

Divine Simplicity was appealing for a few reasons. First, if God is composite in no way, then it seems as though many objections to the compatibility of properties of God—say, of omnipotence and omniscience—fail to be objections at all. For if God is absolutely simple, omnipotence just is omniscience (following the example) and vice versa, and if this is the case then to object that omniscience and omnipotence are incompatible would be to object that two things which are identical are incompatible. Aquinas holds to this very view. On Aquinas’ view, “His [God’s] existence is also His goodness, wisdom, justice, omnipotence, and so on” (22). Second, if God is perfectly simple, then it seems as though God as a hypothesis, if you will, increases in merit, granting Occam’s Razor. For, if God is absolutely simple, then to object to God’s existence as being too complex (as some do) is entirely specious, as God is not complex at all. Third, philosophical interest in Divine Simplicity had me longing to learn more about it.

Hughes’ analysis and critique of the arguments for Divine Simplicity are fantastic. His capabilities in discerning and detailing the complexities involved in Thomistic Philosophy are spectacular. It is his unbiased analysis, however, which most characterizes CTSG. Throughout pages 28-57, he destroys (in my opinion) Aquinas’ arguments for Divine Simplicity. Then, he argues that God cannot be identical to His insular attributes, which counters the argument in defense of Divine Simplicity that, roughly, ‘omnipotence and omniscience may appear to be different, but perfection of either quality shows that they are actually the same’ (60-68).

Yet despite his rather convincing arguments against Divine Simplicity as drawn out by most proponents, Hughes also outlines a possibility for a defense for that very idea. For if 1) God exists necessarily in the logical sense, and 2) if all things are contingent upon God’s existence (two premises Hughes disagrees with, but does not offer an argument to refute per se—instead he refers to Humean thinking as a reason not to accept 1)), then

“[b]y 2), any individual substance in world w distinct from B exists there only at the sufferance of B, and would not have existed if B had exercised its will in a way it might have. By 1), we know that there is an individual substance—the individual in our world which is (a) God—which exists in w, and does not exist at the sufferance of B, that is, could not have failed to exist through any possible exercise of B’s will. It follows that the  individual who is a God in our world is identical to B. Since B and w were chosen arbitrarily, we may conclude that nothing actual or possible could have the specific nature Deity without also being the very same individual as God. In other words, God’s individual essence is no different from His specific essence” (99).

This allows the defender of Divine Simplicity a “way out,” if you will. For she can hold that 1) and 2) are both true, and then argue (though, as Hughes notes, in “a flavor more Leibnizian than Thomistic” [100]) that God exists and his specific and individual essence must be identical. This allows for a modification of Divine Simplicity which avoids the downfalls Hughes points out in the other formulations.

Another fantastic section of Hughes’ work is his defense of omniscience. He suggests (following David Lewis) that omniscience can be defined as “X is omniscient if and only if X knowingly (that is, in such a way as to satisfy the conditions for knowledge) self-ascribes all and only those properties that X exemplifies” (126). This suggested definition of omniscience has much to recommend it. First, it clearly avoids any problems with the supposed incompatibility of a timeless deity and knowledge, thus allowing those who favor Divine Timelessness (such as myself) to have an adequate, defensible view of omniscience. Second, it allows for the compatibility of a timeless, changeless, and omniscient deity (127).

The rest of CTSG is made up of Hughes analyzing Aquinas’ view of the Trinity and the Incarnation. This covers approximately half the work, but I feel the need to sum up Hughes wonderful analysis simply by saying that it seems he has shown there are serious problems with Aquinas’ formulation of the Trinity, granting Aquinas’ presuppositions about identity, simplicity, etc., but it seems that Hughes “way out” for the defender of Divine Simplicity outlined above could potentially be a “way out” for those desiring to defend the Trinity and the Incarnation on a modified account. Hughes himself offers possibilities for defending each of these doctrines which may not necessarily require abandoning Simplicity (cf. 251-253 for one example). As it stands, however, it seems that Aquinas himself has not provided an adequate defense of the propositions he wishes to claim as “compossible.” Rather, defenders of Thomistic philosophy must turn outside of that realm–towards analytic or Liebniz–to reconcile those doctrines which Aquinas wishes to defend.

Hughes does a simply fantastic job of outlining Aquinas’ arguments, analyzing them, critiquing them, supplementing them, and then providing a final analysis. Hughes remains fair and, I would say, unbiased throughout his work. He allows for the possibilities that central theses of Aquinas’ “philosophical theology” are indeed correct, granting formulations Hughes himself does not share. I, however, do share many of the premises of those who can defend Divine Simplicity, and therefore continue to find it a “bruised, not beaten” doctrine. Hughes’ insightful work should command a place of care on any philosopher of religion’s bookshelf, as he has not only written a wonderfully compelling investigation into Aquinas’ philosophical theology, he has also contributed to modern Thomistic and analytic philosophy, but most of all he demonstrated a willingness to concede possibilities on the “other side” of the debate and a rigorous approach to analytic philosophy of religion which one can only hope will be emulated.


Hughes, Christopher. On a Complex Theory of a Simple God: An Investigation in Aquinas’ Philosophical Theology. Cornell University Press. 1989.


The preceding post is the property of J.W. Wartick (apart from citations, which are the property of their respective owners) and should not be reproduced in part or in whole without the expressed consent of the author.

About J.W. Wartick

J.W. Wartick is a Lutheran, feminist, Christ-follower. A Science Fiction snob, Bonhoeffer fan, Paleontology fanboy and RPG nerd.


2 thoughts on “Book Review: “On a Complex Theory of a Simple God” By Christopher Hughes

  1. Try Bradshaw’s, Aristotle East and West: Metaphysics and the Division of Christendom, to plug in Hughes material to the East/West fault line on divine simplicity.

    Posted by Perry Robinson | July 13, 2010, 8:29 PM

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