Short version

I'm specifically referring to Graham Oppy's paper An Argument for Atheism from Naturalism:

Abstract This paper outlines an argument for atheism from naturalism that I have developed in more detail elsewhere (in particular, in The Best Argument against God). The overall shape of the argument is as follows: first, naturalism is simpler than theism; second, there is no data that naturalism does not explain at least as well as theism; and, third, naturalism entails atheism; so we have good reason to prefer atheism to theism. Note that this statement of the shape of the argument is NOT a statement of the argument itself.

In short, Oppy argues that naturalism is simpler than theism, and that, all else being equal, we should always rationally prefer a simpler explanation of the data.

How do Christians rebut Graham Oppy's position?

Longer version

A few relevant quotes from the paper:

Theists differ in the ways that they depart from naturalism. Some theists believe in a God who created our universe ex nihilo. Some theists believe in a God whose actions preserve our universe in existence. Some theists believe in a God who inhabits an eternal realm that has no spatiotemporal relation to our universe. Some theists believe in an intelligent and active God who is neither a natural organism nor an artificial intelligence created by natural organisms. Some theists believe in a God that is a non-personal supernatural power or supernatural force that exerts influence on our universe. Some theists believe that the universe possesses the non-natural property of being divine, or that the non-natural property of being divine ‘permeates’ the universe. And so on.

Although theists differ in the ways in which they depart from naturalism, there is a common feature to theistic departures from naturalism. In every case, theists differ from naturalists by believing in something additional: either believing in one or more additional intelligent agents, or believing in one or more additional forces or powers, or believing in one or more additional non-natural properties of the universe.

Suppose that we are comparing a particular version of theism with a particular version of naturalism. Suppose, further, that these versions of theism and naturalism agree in their beliefs about which natural entities, and natural powers, and natural forces, and natural properties, and natural laws there are. In this case, it’s not just that the theist has beliefs in something over and above the things the atheist believes in; it’s also the case that the naturalist does not have beliefs in anything over and above the things the theist believes in. From the standpoint of the naturalist, the theistic beliefs of the theist are pure addition; and, from the standpoint of the theist, the naturalistic beliefs of the naturalist are pure subtraction.

In this case, if all else is no better than equal, then there is clear reason to prefer naturalism to theism. For, if all else is no better than equal, then there is no reason to have the additional theistic beliefs. Hence, in this case, in order to decide between theism and naturalism, we just need to determine whether all else is no better than equal.


The burden of the rest of this chapter is to argue that there are no features of the natural universe that have a better explanation on theism than they do on naturalism. Of course, I won’t be able to examine every feature of the natural universe that might be thought to have a better explanation on theism than it does on naturalism. However, I shall try to examine all of the most prominent features of the natural universe that have been widely supposed to have a better explanation on theism than on naturalism. Given the treatment of the cases that I do discuss, it should be obvious how to extend the discussion to features of the natural universe that I do not examine here.

He then goes on to explain how 8 features of the world commonly used to argue for theism can be better accounted for under naturalism. Namely:

  • Existence
  • Causation
  • Fine-Tuning
  • Morality
  • Consciousness
  • Miracles
  • Religious Experiences
  • Meaning and Purpose

9. Conclusion
As I mentioned at the outset, I cannot claim to have considered all of the data that bears on the decision between theism and naturalism (and not can I claim to have given a fully adequate assessment of any of the data that I have considered). However, I hope that I have done enough to indicate how my argument for naturalism would look if it were set out in full and complete detail. (I give a fuller—but still incomplete—exposition of the argument in The Best Argument against God, Palgrave-Macmillan, 2013.)

10. Note about Evil
Of course, there is data that at least some theists suppose favours naturalism over theism—e.g. data about horrendous suffering, data about non-belief, and data about the scale of our universe. Some naturalists think that data about horrendous suffering is logically inconsistent with theism. As Epicurus argued long ago:

Is God willing to prevent evil but not able? Then he is not omnipotent. Is he able but not willing? Then he is malevolent. Is he both able and willing? Then whence cometh evil? Is he neither able nor willing? Then why call him God?

Other naturalists think that data about horrendous suffering renders theism highly improbable: given the major horrors of the twentieth century alone, isn’t it incredible to suppose that our universe is the work of an omnipotent, omniscient and perfectly good being? I have focussed on data that many theists suppose favour theism over naturalism because my argument requires only that, on any piece of data, naturalism does at least as well as theism in explaining that data. Even if it is true, for example, that naturalism affords a better explanation of horrendous suffering in our universe than is given by theism, that truth makes no contribution to the argument that I have been advancing here.

NOTE: Graham Oppy's formulation of the argument is arguably one of the strongest available in the literature, given Oppy's reputation as one of the most respected contemporary atheist philosophers. For instance, William Lane Craig once said about Oppy's book Arguing about Gods:

Oppy's book is not merely recommended but essential reading for anyone interested in natural theology today. No one can pretend to a successful theistic argument unless he has dealt with Oppy's criticisms first. (source)

However, the claim that naturalism is "simpler" than theism is thrown around quite frequently in informal discussions with atheists. For example, take a look at some of the answers to Could Occam's Razor ever favor theism?.

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    There are much better arguments for atheism, this is laughably weak. Occam's razor is to be used as a tool to prioritize how we analyze various models, it's not something which can be used to prove or disprove something. A flat, stationary Earth is simpler than a spherical rotating one which also orbits around the Sun and around the center of the galaxy. Yet this does not prove that the Earth is flat or stationary.
    – vsz
    Commented Mar 1 at 8:48
  • @vsz "There are much better arguments for atheism" - For example?
    – Mark
    Commented Mar 1 at 13:15
  • For the morality argument, I suggest C.S Lewis' book Mere Christianity. It does a great job of laying down a philosophical argument for theism.
    – Seggan
    Commented Mar 1 at 16:39
  • I hold no brief for any God yet I ask, do you not see there could never be a winning, nor even a realistic argument for atheism? That is quite separate from any argument in favour of any god or gods. Do you know an atheist argument which doesn't boil down to one of three things: 'There is no evidence for God' or 'How could your God allow (whatever) to happen?' or 'What need is there for a God?'? Please be sure, in my view all theist arguments are equally meaningless, and I suggest that's not the point here. We all have our own beliefs, none of which is susceptible to proof. Commented Mar 3 at 20:57
  • One of the best recent authors in Natural Theology and relationship between Theology and Science is Alister McGrath. His 2008 book The Open Secret: A New Vision for Natural Theology looks very relevant and well positioned to counter Oppy's naturalism. Commented Mar 5 at 6:27

4 Answers 4


If an intelligent observer like William Lane Craig thinks this is the strongest argument for atheism out there, then it makes me feel quite a bit more sound in my belief in God, because it is almost laughably weak.

Matthew's answer more than adequately addresses why the appeal to Occam's razor here is fallacious.

I'll go through each of Oppy's 10 points in the paper and point out where they fail, even if we completely accept Occam's razor:

1. Existence: Here Oppy makes a fundamental misunderstanding common to naturalistic philosophers. If the universe requires an explanation for its existence, why doesn't God? For the simple reason that, by definition, God is uncreated. A created demiurge is not God. This is a fundamental tenet of all monotheistic worldviews. Thus, we are comparing two postulates: The universe in all of its complexity, simply exists for no discernable reason. Or God exists by virtue of his self-existent nature. The second at least has its explanation. Furthermore, viewing things from this perspective, Occam's razor favors theism. If we believe in divine simplicity (which I do), then postulating the existence of God is only one postulate, while the existence of the natural world and all its laws seems a lot more complex. On the other hand, it's hard to believe that the physical laws and the existence of the material universe is reduceable to a single postulate.

2. Causation: As the paper points out, this is pretty similar to existence (see above). Oppy is correct that, at least as regards the problem of a regress of causality, an uncaused primordial universe and an uncaused God are equally good explanations. Though, for the same reasons outlined above, Occam's razor favors theism as it postulates only one primordial cause, while naturalism cannot make a similar assertion. A naturalist might believe that the universe originates from a single primordial cause at the base of the chain of causality, but this cannot be proven scientifically.

3. Fine-Tuning: Oppy makes a fair point here. The naturalist must assert some brute facts, why not simply assert the fine-tuned universe as one of them? That's logically sound, but I can't imagine finding that a more satisfying answer than asserting a wise creator. And again, here we see a fundamental paradox for the atheist: Fine-tuning requires the atheist to either believe in some unimaginably unlikely coincidences or that brute facts of the universe to themselves be complex and interconnected, in which case Occam's razor clearly favors the theist, who makes only one assertion of brute fact: God is.

4. Morality: Oppy here obfuscates to the point of near-incoherence. If I might translate his argument, I believe it goes like this: "Theists and atheists alike must postulate that morals originate, ultimately, from some objectively real source values that are not explained in terms of anything else. On a logical level asserting brute existence of some morals is no better or worse than than asserting they originate from God's goodness." Fair enough. (Though, again Occam's razor here clearly favors the theist, who with one principle has explained existence, causation, fine-tuning, and morality, while the atheist must introduce at least one new principle for each.)

Additionally, Oppy discards his own naturalistic view in this point, by introducing a concept of "good" into the picture. Tell me, O naturalist, where in this universe, which you assert is "all that there is", can I find this "good"? Oppy alludes to the Epicurean moral formulation that pleasure is the basic good from which all moral principles arise. Fair enough, but it requires assertion of some non-material good in order for this to motivate people to be concerned about the pleasure of other people. If I derive pleasure from torturing infants, clearly some stronger moral principle is needed to say this is bad for me to do. (One might argue that to do so takes pleasure away from the infant, bur keep in mind that this is not relevant to my pleasure, so in making this argument you must assert some additional principle of "equality of human lives" or something like this. If this seems very extreme, it is not. This is almost exactly the content of the debate on ethics of abortion. The pro-abortion argument's logic would also justify infanticide or even murder of adults, but for the additional assertion that lives of born people are valuable enough to negate the pleasure principle of morality.) An atheist may assert existence of moral facts, but a naturalist cannot without sacrificing consistency.

As an aside, I would mention that Oppy's assertion that "typically...theists suppose that pleasure is good" (p.5) belies substantial ignorance of theistic philosophy. For just a couple examples that I am peripherally familiar with: Aristotle taught the pleasure is neither good nor bad, but instead is a signal to the conscious mind that something good is happening (though this signal is unreliable if your beliefs about good and bad are perverted). Epictetus taught that pleasure is entirely irrelevant to ethical questions. Given that both of these (theistic) philosophers have been hugely influential in history of Western theistic philosophy, this is not a good sign for Oppy's knowledge of the field. (I must admit I seldom read modern authors, so I can give Oppy the benefit of the doubt. There may have been some vast change in thought among theists in recent times that I am unaware of, and Oppy is here referring to modern thinkers only.)

5. Consciousness: I think consciousness is not well-defined enough to assess Oppy's argument here.

6. Miracles: Oppy's argument here is passable, as far as it goes. Naturalists use one explanation to explain away all reports of miracles: The reports are inaccurate. Theists assert most are inaccurate, but sometimes they are accurate. As regards this point, the naturalist finally has Occam's razor on his side.

We should not let it slide here that "miracle" must be defined. I do thousands of things every day that any person a thousand years ago would call miraculous, even something as simple as typing this answer and sending it, in an instant, to thousands of people around the world. The true explanation of this can be done without invoking any violation of the natural order as we understand it. However, the same can be said of all other miracles. After all, to a theist, what is the natural order but that God directs all things? When a miracle happens, it is because God has decided to do something differently from his usual way. But God is not any less active in the "non-miraculous" than he is in working miracles, and thus, in a theistic worldview, miracles are not "unnatural" but "supernatural". As soon as we recognize that nature is not all there is, nothing is more natural than miracles.

Also, it should be noted that in many cases, naturalistic explanations of accounts of miracles are quite a bit more convoluted than the claim that the miracle actually happened. Most notable here would be Christ's resurrection, which naturalistic accounts of are often pretty absurd and only reasonable if we begin by assuming that naturalism is true.

7. Religious Experiences: Oppy's argument here is fair. But it does not explain something a little more fundamental, which is the question of why do people seem to have an instinctual attribution of such experiences to the supernatural? C.S. Lewis calls this the sense of the numinous, and gives a great description of it in chapter 1 of The Problem of Pain. Why, in a naturalistic worldview, do we alone of all animals have an instinctive sense of the reality of nonmaterial things? It's a bit hard to account for. Harder if you yourself have experienced the numinous.

In the face of the existence of these numinous, "hard-to-interpret experiences", it seems perfectly rational to say that human beings were designed with a capacity for spiritual experiences because such experiences reflect some nonmaterial reality. If people are prone to misinterpret these experiences, that has no bearing on the possibility of their real nonmateriality. In any case, it is clear that on this point, the naturalist has no advantage over the theist.

8. Meaning and Purpose: It's a little odd for Oppy to invoke Aristotle, a theistic philosopher, to defend a "naturalistic" view of meaning and purpose. He is correct, however, that Aristotle's view of meaning and purpose does allow nontheists to live meaningful lives. However, it is not possible for the atheist to account for the existence of meaning and purpose the way that a theist can. The modern naturalist, I suppose, must conclude from Darwinian evolution that the "meaning and purpose" of life is to propagate one's genes. This is a little more magnanimous than Epicurean pleasure-based ethics, as it accounts for why you ought love your family and it even gives some reasonable basis for desiring a stable society in the long term.

Practically speaking, however, it's notable that atheists have far fewer children on average than religious folks. Clearly, few people actually take notions of "purpose" and "meaning" from naturalism. Nor does Oppy claim do to so. Rather, as he does with morality, he discards naturalism here in favor of some objective nonmaterial reality of "meaning" and "purpose".

He does correctly identify that Christianity takes "purpose" and "meaning" to an extreme level by granting us "participation in an epic cosmic melodrama". I think it's clear that this Christian view lends more purpose and meaning to life than Aristotle's view does (which, in turn, is more meaningful than Darwinism), but that isn't an argument for Christianity's correctness. After all, it is pretty easy to read too much meaning into things that are actually more shallow. We do this all the time. The claims of Christianity certainly dial the "meaning and purpose" up to 11 in a way that other philosophies do not (even most theistic ones), but the relevant question is not whether this is extreme but rather whether it is true.

Summary: Contrary to Oppy's claims, theism trounces naturalism by the standard of Occam's razor. Monotheists use one single principle to account for all of existence, causation, fine-tuning, morality, meaning, and purpose, while atheists must introduce at least one new principle on each of those points (and usually more than one). The only point where Occam's razor does seem to favor the naturalist is as regards miracles, but even here the argument is weak. Oppy also turns his back on strict naturalism in order to account for morality and meaning. (In this way, Oppy's point of view is more complex than the theism, according to his own standard. He asserts two fundamental nonmaterial realities, i.e. ethics and meaning, while the theist only asserts one, i.e. God.)

I think Oppy's arguments could be vastly improved by not asserting that naturalism makes for a simpler model of reality (because it does not), but rather asserting that naturalism requires the least amount of deductions from the observations about the material world. Naturalism sets a boundary that forces everything that we can observe to be explained in terms of things we can observe. This model of reality is far more complicated than theism in terms of its assumptions, but it has the advantage of limiting their distance from our ordinary day-to-day experience. However, by taking just one step outside the realm of the visible, we derive a much simpler and more beautiful model of reality.

It reminds me somewhat of Goodstein's theorem, which describes a true property of numbers that can be checked individually for each number, but to unify the picture a mathematician must take a step outside the realm of the finite and perceive the bigger picture, which he will find to be simpler, more powerful, and more beautiful.

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    Excellent answer, +1. To be a bit more fair to Oppy's arguments, William Lane Craig was referring to Oppy's book Arguing about Gods, which has 472 pages. He also published another book titled The Best Argument against God, with 101 pages, where he developes the arguments presented in the paper in more detail.
    – Mark
    Commented Mar 1 at 0:45
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    I see. After reading the paper though, I doubt that such arguments are salvageable... Perhaps I'll take a look some day, but apologetics generally doesn't interest me that much. Commented Mar 1 at 1:22
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    "typically...theists suppose that pleasure is good"... may be true for theists, whoever they are, but it isn't very true for Christians. (At least, not in the way I suspect Oppy is claiming.) Anyway, very thorough! +1 Incidentally, kudos on your handling of #6; I recently made the same point over at Philosophy.
    – Matthew
    Commented Mar 1 at 5:56
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    @DarkMalthorp Thomists also deem pleasure is good, and better than honor and wealth, though pleasure need to be pursued while aiming for the "ultimate end", and the activity has to be done "in God", thus implying virtuous pleasure. Thomists would also say that Oppy does correctly identify that Christianity takes "purpose" and "meaning" to an extreme level by granting us "participation in an epic cosmic melodrama". I like how Oppy relabels the apocalyptic vision of Christianity. Commented Mar 1 at 14:11
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    Not even a Christian here (Muslim), but I appreciate many of your points and find them rational. In my opinion, any and all forms of theism are more rationally plausible than atheism, and I must repeat what you said that if the arguments presented by Oppy are some of the greatest ones from atheism, then they are truly hilarious. Commented Mar 3 at 18:49

Let's take the first two points one at a time. (The third is only relevant if the first two are correct, which, as we'll see, isn't the case.)

  1. Naturalism is simpler than theism.

This is true! It's also irrelevant; simplicity is not necessarily a measure of correctness. (Ironically, there is no naturalistic reason to expect "elegant" explanations; the idea that simpler explanations are preferable is to some degree dependent on theism.)

As an example, Newtonian physics are certainly simpler than Einsteinian physics... but practically no one uses this as a basis to argue that Einsteinian physics are incorrect. Therefore, this argument is both true and irrelevant.

  1. There is no data that naturalism does not explain at least as well as theism.

Excuse me; my sides hurt from laughing so hard.

While there are reasonable objections to just saying "God did X", in terms of simplicity, "God did X" far exceeds some of the absolutely insane explanations that Materialism is forced to concoct for some phenomena. (Ahem: "dark matter"?) Thus, ironically, the first principle undercuts the second.

The larger problem, of course, is that the second simply isn't true. It takes a dedicated commitment to systematically excluding theistic explanations to believe that material explanations are somehow "superior". In fact, this is so challenging that even some materialists find it hard to swallow. Meanwhile, less close-minded people recognize that theistic explanations are far less ad hoc, and far more consistent with the available evidence. (I'm not going to elaborate here; there are plentiful resources available to anyone that bothers to look.)

In every case, theists differ from naturalists by believing in something additional.

So what? At one point, we didn't know what electrons were. Imagine what the state of chemistry (not to mention all the fields that deal more directly with electricity) would be like if someone had said "this idea of an electron ought to be rejected because it adds 'something additional' to what we know about science".

There also seems to be an argument to the effect that we shouldn't believe in "something additional" because people can't agree on exactly what is "additional". But there have been plenty of scientific controversies in the past that have eventually been resolved, and there are some in the present that are yet to be resolved. No one has a solid explanation for abiogenesis, and yet materialists are (wrongly) confident it must have occurred. If they were consistent, they would look at that disagreement and conclude that their fundamental premise is flawed. The mere existence of disagreement doesn't establish that one side or another must be correct.

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    Well said, but I question the concession of the point that "atheism is simpler." While it is true that "there is no god" is simpler than "there is a god" in terms of the things which exist, theism is simpler in the sense that it postulates only one brute fact, i.e. God's existence, whereas naturalism postulates as a brute fact the highly complex universe we live in and its physical laws. Commented Feb 29 at 20:30
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    @DarkMalthorp, hmm, fair point! Still, when it comes to actually explaining things, you end up pulling in the known laws of physics for either case. Say, then, that materialism's world model is (in theory) simpler. In practice, the contortions they have to make to account for stars, life, etc. result in what can be politely called "a mess", but there's at least some point at which one can stand and say "this looks simpler", as long as one doesn't look too closely. At any rate, I don't find it necessary to argue that point.
    – Matthew
    Commented Feb 29 at 20:52
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    Upvoted for your excellent opening point. But a far stronger answer is that theism is not a competitor to naturalism in explaining the natural world. (Christians should be very wary of being drawn into this conflict narrative - God of the Gaps.)
    – Ian Goldby
    Commented Mar 1 at 13:53
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    @IanGoldby indeed, many notable scientists and mathematicians (Newton, Clerk-Maxwell, Boyle, Euler, Mendel, Riemann, etc, etc) were theists, Christians even. That did not stop them from investigating the natural world.
    – Seggan
    Commented Mar 1 at 16:50
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    @IanGoldby, it depends what is meant by "naturalism". The methodology was created by theists. When it becomes a dogma, however, it absolutely is a competitor. It matters what, exactly, one means when they say "naturalism". (This Answer to a question over on Philosophy may be relevant.) In this instance, I am fairly confident that what we're talking about is metaphysical (dogmatic) naturalism, a.k.a. materialism, so it is correct to treat it as a competitor.
    – Matthew
    Commented Mar 1 at 17:25

Disclaimer: I haven't read yet the 2 references you provided (one short and one long) but due to your diligent presentation of the problem (along with the quotes), I would like to take a stab at it, from which you can comment for me to improve this answer further. So this is just a very early draft.

We are entering a new age of apologetics which emphasizes a pastoral angle, exemplified by Tim Keller who passed last year, where the #1 rule is compassion and understanding of the psyche of unbelievers in "all cylinders". One feature of this new age is thus a renewed attempt to understand the psychological and philosophical life context of individual unbelievers (thus intense listening) instead of simply proclaiming an exegesis of Bible verses (the evangelism side), or worse, pronouncing judgment for those who de-converted (see the exhortation toward the end of Gavin Ortlund's recent video Analyzing Rhett's Deconstruction), Gavin Ortlund being another representative of this new age of apologetics.

This then requires the study of history of philosophy, of psychology, and of neurology and then develops a Christian answer in terms of those findings. Your question then, represents one of the best statement of the problem, formulated in terms of the 8 features of the world, which I commend highly, making it easy for Christians committed to this new age of apologetics to answer.

Before I engage the references, what jumped to my attention is the last feature: "meaning and purpose":

  • In my understanding of naturalism, while there can be discerned a "purpose" within the world, it is too vague, although Aristotle's study of the human nature DOES have a partially full Christian answer (i.e. his teaching on telos), which Aquinas then carried it to completion by proposing God to be the "ultimate end" (ultimate telos).

  • As for meaning, isn't nihilism the logical conclusion of naturalism? If not nihilism, then it's giving up the hope of finding an objective meaning that applies to every human being for all cultures. Again, Aquinas saw this problem of the meaning of human life early on, and for 800 years, his Christian solution is STILL persuasive, that life in a resurrected glorified body in close fellowship with God is the ultimate meaning awaiting us when God destroys this universe at the end of age and re-creates a "new heaven and earth" for us glorified humans to inhabit. Without this hope, there is not much meaning to human suffering and human injustice, other than the meaning that different persons subjectively or different communities communally construct for themselves. For a lot more about Aquinas's solution, listen to this "Man & the Meaning of Life" set of 26 lectures especially the lecture The Search for Happiness: Wisdom from Aquinas and the Classical Tradition.

(to be continued per comments and reading the references)


To complement the already posted answers, I think the following paper is undoubtedly relevant as regards the simplicity premise of Oppy's argument: Ockham on the Side of the Angels: Why a Classical Theist Shouldn't be Moved by Oppy's Argument from Simplicity, by Tyler McNabb and Michael DeVito:


A common argument put forth by naturalists (including the prominent philosopher Graham Oppy) in support of naturalism as a worldview over theism, is to claim that naturalism is a simpler hypothesis. Theism posits the existence of everything that naturalism does, plus the existence of a theistic realm. Thus, all things being equal, via Ockham's Razor, naturalism should be preferred to theism. In this essay, we argue that the Classical Theist need not worry about the naturalist's Simplicity argument. Specifically, we argue that, the one holding to a scholastic metaphysics (i.e., potency-act distinction, participatory metaphysics, and existence-in-degree), in the end, will be the one with the simpler worldview.

The naturalism-versus-theism dialectic features numerous arguments and counter-arguments stemming from all areas of philosophy. One prominent battleground focuses on the concept of simplicity – specifically, trying to determine which worldview can account for the various features of our reality, while, at the same time, utilizing the fewest metaphysical (epistemological, semantical, etc.) concepts in order to do so. The idea being, all things being equal, the simplest solution is generally the best solution (a principle often termed ‘Ockham's Razor’).

Specific to the natural-versus-theism debate, Graham Oppy remarks, Although theists differ in the ways in which they depart from naturalism, there is a common feature to theistic departures from naturalism. In every case, theists differ from naturalists by believing in something additional: either believing in one or more additional intelligent agents, or believing in one or more additional forces or powers, or believing in one or more additional non-natural properties of the universe… From the standpoint of the naturalist, the theistic beliefs of the theist are pure addition; and, from the standpoint of the theist, the naturalistic beliefs of the naturalist are pure subtraction… In this case, if all else is no better than equal, then there is clear reason to prefer naturalism to theism. For, if all else is no better than equal, then there is no reason to have the additional theistic beliefs. (Oppy, 2018: 2)

As Oppy proceeds to explain, while naturalism is committed to: (1) an account of the natural universe and (2) the natural universe is all that exists; theism, in contrast, is committed to (1) plus (2*) there exists a theistic realm, and (3) the natural realm and the theistic realm are all that exists (Ibid). Thus, all things being equal, via Ockham's Razor, one should favor naturalism over theism.

Let's grant that theoretical simplicity is determined, at least largely, by metaphysical simplicity.1 That is, in comparing hypothesis1 over hypothesis,2 all things equal, whichever hypothesis endorses a more modest ontology should be preferred. And let's even grant that postulating a multiverse in order to accommodate fine-tuning is ontologically simpler than a hypothesis that postulates God and one universe at the level of ultimate reality. While this second assumption doesn't compart with our intuitions about simplicity, we assume it for the sake of argument.

We argue still, that the already committed2 Classical Theist shouldn't find Oppy's argument from simplicity compelling. The proponent of the type of Classical Theism that we have in mind is going to endorse the potency and act distinction, she is going to endorse a participatory metaphysics, and she's going to think that existence comes in degrees. The familiar potency-act distinction distinguishes between the way things are and the way things could potentially be. For example, the coffee on Mike's desk is warm, but it has the potential to be cold (say, if Mike let's it sit on his desk overnight), or the potential to be boiling hot (perhaps Mike rewarms it in the microwave for too long). Potentialities (coldness, hotness, sharpness, dullness, roundness, flatness, etc.) are real features of objects (coffee, pencils, balls, etc.) that have yet to be actualized. Classical Theists think that behind all change is ultimately being that is simply pure act.

By a participatory metaphysics, we have in mind the view that there is a distinction between existence or esse, and essence.3 (For example, the Classical Theist thinks that Pikachu has an essence, but yet, lacks existence.) Existence is what is fundamental to ultimate reality. Unless one's essence is to exist, one's essence has to come together with existence and participate in it. Essences which come to exist in this way, can be said to have derivative existence. These essences can be said to exist, but they exist to some lesser degree. Having said all of this, we can now see why the Classical Theist (at least of the stripe mentioned) shouldn't be convinced by Oppy's argument.

Traditionally, ultimate reality is what is of concern in the debate between theism and naturalism. By ‘ultimate reality’, we simply mean the correct account of the nature of everything or of all being that exists at the highest degreed level of reality. Generally, for naturalists, all objects of our experience, such as humans, houses, and stars, are part of ultimate reality. The Naturalist is then committed to the existence of composites (act and potency compounds) as features making up ultimate reality. The Classical Theist, however, denies this. These things exist but not as features that make up ultimate reality. Objects exist in a derived and less fundamental sense. As to what exists in ultimate reality, theism simply postulates that there is pure act. Theism is then simpler.

Now, let's say that the naturalist gives up on debating about what one posits at the level of ultimate reality. Instead, she will settle for considering what is simply fundamental to her worldview. Recently, several theists have made a similar move. Perhaps she will argue that the existence of quarks or perhaps an initial singularity is what is fundamental to her view. There's no need to worry about anything else she says. Nonetheless, quarks or an initial singularity would still be reducible to act and potency compounds. In contrast, what is fundamental to the Classical Theist's view is simply pure act. Either way you slice it then, the Classical Theist won't see the need to abandon ship.

OK, the naturalist says. Let's not determine simplicity by way of what's fundamental to the respective hypotheses, but rather, let's determine which hypothesis is simpler by an analysis of all things one postulates, even if those things don't makeup ultimate reality. Perhaps this is how we should have understood Oppy this whole time. The naturalist postulates composites while the theist postulates both pure act and composites. Naturalism is therefore simpler.

Not so fast. This might move the naturalist, but this scenario won't get off the ground for the Classical Theist who endorses participatory metaphysics. Recall that the Classical Theist thinks that in order for some essence to exist, it must participate in existence itself. If the theist equates pure existence with pure act (as they normally do), then she will take it that the naturalist is already committed to both the existence of pure act and the existence composites. Of course, the naturalist might not be convinced that pure act just is God, as there is the whole problem with the second-stage of arguments for God's existence. We needn't get into all of this here. Nonetheless, the question that is being debated is whether an already committed Classical Theist should be convinced by Oppy's argument. If the Classical Theist assumes participatory metaphysics, then she needn't concede of a possibility where one can have existent things without existence itself. Participatory metaphysics is part of the Classical Theist's background knowledge, k. The Classical Theist likely thinks alternative metaphysics of existence are incoherent and, for completely independent reasons, implausible. To be moved by Oppy's argument from simplicity, what is needed are additional reasons to reject k. Only upon developing these reasons, will the Classical Theist find Oppy's simplicity concerns more credible.

Now, we want to clarify, that our response here shouldn't be seen as an argument for Classical Theism. We recognize that one could argue that if we assume the sort of participatory metaphysics discussed here, then we are already assuming the existence of God and the simplicity concerns become irrelevant. Now, we don't think this is necessarily the case due to there being a second-stage or gap problem from arguing from pure act to God. But as mentioned earlier, this needn't concern us here. What's important is to clarify that we are simply arguing that Classical Theists who accept the aforementioned theses won't find Oppy's Simplicity argument compelling because of the metaphysics they assume. In fact, the Classical Theist might be turned off (perhaps rightly) to the idea that we can even in principle prove or disprove God's existence by way of looking at Classical Theism as a scientific hypothesis. Since God is, after all, not a thing or an object of the universe, why think that scientific methodology plays a role in establishing what grounds the realm of existent things? Nonetheless, even if we concede that such methodology is appropriate, we have shown why Oppy's argument from simplicity shouldn't move the Classical Theist of the stripe that we have imagined.

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    Useful answer, +1. Re And let's even grant that postulating a multiverse in order to accommodate fine-tuning is ontologically simpler than a hypothesis that postulates God - having gone a ways down the multiverse rabbit hole I would not grant that the naturalistic multiverse is simpler. Also, so sorry to hear that Pikachu isn't real.... Commented Mar 5 at 0:28
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    Unless of course Pikachu exists somewhere else in the multiverse =) Commented Mar 5 at 0:51
  • @HoldToTheRod, would you like to participate in this question?
    – Mark
    Commented Mar 6 at 13:39
  • thanks for the cordial invite; I'll pass on that one. Commented Mar 7 at 18:33

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