Some definitions and assumptions:
God: classic theological entity defined as “omniperfect”. Usually God is said to have perfect goodness, perfect power, perfect knowledge, and perfect existence. Theists say that God has always existed and, moreover, is involved in the moral sphere, usually carrying out some kind of ultimate plan for Cosmic Justice, as well as bestowing “freewill” to human souls. Alternatively, God could be finite, perhaps as a very powerful galactic being with the power of fine-tuning universes as a kind of detached tinkerer, but without any personal concern for individuals, or as some limited panentheistic process-God.
While interesting from a theoretical perspective, I don’t take this finite or limited concept of God to be worth talking about in spiritual terms, as it seems to be compatible with naturalistic metaphysics. Hence, I will reserve the term “God” for the “omniGod” of classic theology since that is really the metaphysical opponent for naturalistic metaphysics (since we can imagine a finite but really powerful being creating a universe). But naturalism is not compatible with the existence of the omniGod, who has been understood to be the “ground” of everything that exists, whereas in naturalism the natural world does not ontologically depend on a “higher power” to exist; it subsists on its own just fine.
Naturalism: the view that there are no supernatural miracles, supernatural entities, or supernatural realms (such as Heaven, Hell, or Limbo, etc.). Naturalism is the theoretical framework, worldview, or reality map that all phenomena are natural phenomena. There is no “spiritual” or “divine” kind of existence, except in our brain-generated imagination, which has culturally inherited mythological concepts from prescientific ancestors and their primitive belief systems. Naturalism is not necessary committed to a “lawful” ontology (i.e deductive-nomological explanatory frameworks) wherein all phenomena are covered by general law. Another possible explanatory framework compatible with naturalism would be a “model theoretic realism”, or a “case study theoretic”. Naturalism, most simply put, is the view that all that exists is the natural realm.
Naturalism is not committed to the idea that the universe was “created out of nothing” from the Big Bang, since “oscillating” models are logically possible wherein the universe, in some form or another, has always existed in the way that God has always existed. It’s just always been there. Since theists can imagine an endless future (life in Heaven), they must also be able to imagine a past without a beginning. Just as we can imagine adding “one more day” onto the future forever in heaven, we can imagine “the day before” forever backwards. This poses no conceptual difficulties. Moreover, naturalism could explain all our empirical evidence. Any experience of God can just as easily be explained as a hallucination or delusion as it can be explained as actually being an experience of a divine being (which would require adding the supernatural realm into your model). How could that person ever really be certain that it was an experience of the divine rather than just a by-product of neural activity which causes them to have an “other worldly expereince”? Certainty and absolutism in knowledge claims (“I just know I am right!”) has a terrible track record. Being absolutely certain you are right about how to think about a concept stops the doubting process that underlies the true scientific attitude, which is inquiry driven from lack of certainty.
Atheism: An atheist is a person who does not believe in God (but not necessarily someone who claims to have “proved” that God doesn’t exist). The atheist does not think that “existence” is more perfect that “nonexistence”, and thus denies the ontological argument that God must necessarily exist since He has perfect existence. Even if existence is more perfect than nonexistence, this would be compatible with the idea that a natural world that exists would be better than a natural world that didn’t exist, and that an existing natural world would be the “greatest thing conceivable”. The atheist doesn’t have to be a naturalist, but I think that any well educated modern atheist should embrace naturalism. After all, God as a concept was used to answer metaphysical questions like, “What is the ultimate nature of reality?” If you reject God, how are you going to answer those ultimate questions? Naturalism is the obvious choice to replace ontotheology for the educated atheist given everything we know about the natural cosmos.
Now, the evidence for a cumulative case for the truth of naturalism and atheism:
- Methodological naturalism.Scientists usually adopt methodological naturalism to do science. Science has been incredibly successful (e.g. iphones, lasers, space programs, computers, the aviation industry). Why is science successful? Is it because God holds the universe together through divine fiat, executing a perpetual miracle or having perfectly wound the watch at the beginning of the universe? Or is science successful because naturalism is true? I believe that inference to the best explanation that we can currently come up with based on hundreds of years of sustained inquiry is that science is successful because the methodological naturalism underlying science is ontologically true, or at least approximately true according to our most corroborated hypotheses and theoretical frameworks. The competing alternative hypothesis is that science works because God exists. The problem with this alternative hypothesis is that there cannot be a science of divine acts. Anyone who claims certain knowledge of the divine realm and how it really works is fooling themselves; as long as neural explanations can predict behavior (e.g. the “God helmet“), then we cannot use “personal experience” of the divine as evidence that the divine realm actually exists. There are better, more parsimonious explanations and ontological frameworks to explain why people experience the divine realm. I think that a world by itself is more eloquent than a world plus a divine realm, which is a historical relic of three tiered prescientific folk metaphysics (the Human world in the middle, the Underworld below, and Heaven above, where the gods live). If we are going to predict the behavior of a system that we collectively and intersubjectively come across in experience, we must assume that the system is natural and subject to the formation of patterns and regularities (e.g. the regularity of the molecules in a grain of salt, or a boulder). Moreover, the biological world is full of repetitions, habits, and rhythms. We are developing the conceptual tools to study systems, not just in terms of regularity, but in terms of deterministic chaos. Scientific explanations are better than divine explanations because the scientific explanations lead to novel predictions, which are then confirmed by empirical evidence and integrated with previous knowledge and theory. While it’s possible that God has given his believers divine revelations as to the truth of His existence, there is no way to argue it’s impossible that the true explanation of divine revelations is that they are simply hallucinations triggered by neural activity, which in turn can be stimulated by ritual, prayer behaviors, religious ceremonies, drugs, fasting, communal singing, etc. (See the book Inside the Neolithic Mind:Consciousness, Cosmos, and the Realm of the Gods). The question then is which hypothesis is more probable?
- Problem of evil. The problem is that I can easily conceive of a world better than this one that was created by an omniGod. There is an overwhelming amount of suffering and cruelness that happens in the universe independently of any moral/intentional influence of humans, especially if evolutionary theory is correct about the origins of species (which it is). I don’t see how predation works to the good of anything. I can imagine a God creating a much better world that still allows an arena for humans to make mistakes and learn to be responsible, and make their souls “greater”. But birth defects? Predation? Tsunamis? Earthquakes? Floods? Genetic diseases? Predation? I don’t take Original Sin very seriously. It explains nothing. Only science offers any hope of stopping the suffering of these devastating natural disasters. Sure, science can spawn evil very easily, but how does praying to make the world a better place do anything constructive? Praying to gods won’t get us anywhere in this world. The naturalistic perspective is the only thing that makes sense of out all this evil and suffering. Through science we can understand our place in the overall scheme of things and answer fundamental questions about ourselves e.g. where did we come from? How old is the Earth? What’s out there? What’s our relationship to all these animals (especially great apes)? When a lightning bolt starts a forest fire and cruelly kills innocent animals, why did that happen? Naturalism is the best explanation, for such phenomena are confusing from the theistic perspective. They can only appeal to ignorance for “God works in mysterious ways, it’s possible that it will all work out for the best in the end.” But possibilities are weak evidence for the theistic side, since the atheist can appeal to the explanatory framework of naturalism and offer more convincing explanations for the massive suffering around us (evolution, natural selection, geology, meteorology , genetics, modern medicine, etc.). It’s a cruel world, no doubt. But at least naturalism helps us understand it, and gives us a true sense of the contingency of natural existence and the fragility of individual existence, and shows us why life on earth is worth preserving.
- Free will. It is often said by theists that without free will we could have no moral responsibility, because unless you freely chose to act this way and not that way, you cannot be held responsible for your action. And if the will is “freed” from the physical constraints of embodiment, this seems incompatible with a naturalistic worldview. And since no one can deny that you have the ability to freely choose your actions (such as opening and closing your fist at will, or deciding to stop at the store on the way home from work), we have reason to believe that there is more to reality than just the physical universe. Theists claim that our freewill proves that God must exist and that there is an absolute moral order on the supernatural plane of existence. Case closed right? Not so fast. There is no denying that humans have a will or make decisions, but what reason do we have to think that the will is free? If we can come up with a plausible naturalistic model for the will, we will be able to talk about willing and making decisions without supposing that the will is “free” from the physical constraints through which it is realized. As it turns out, we do have such a model. Psychologists are starting to form a consensus that there actually exists two decision-making systems in the human psyche: System 1 and System 2. System 1 is fast, automatic, prereflective, emotional, inherits most features from phylogeny, is domain specific, heuristic, and executes its mentation in a massively parallel way. This is the system that will make you instantly “decide” to make a value judgment that a dark alley is dangerous, increase your heartbeat, and decide to walk faster. In contrast, System 2 is slow, consciously controlled, reflective, linear, narratological, multimodal,”global” articulate, and inherits most features from ontogeny, culture, and learning (plasticity). Most psychologists agree that in all likelihood, System 2 is only available to humans, and possibly, in a limited respect, to a few other higher mammals (like Great Apes). To me, System 2 decision making is exactly analogous to what theists are referring to when they talk about free will. Yes, we have the ability to step outside the domain specific context of our perceptual-emotional context and reflectively deliberate on how we should act, possibly in terms of abstract rules and principles. But this is not evidence for a soul, God, or any supernatural phenomena. Willing and deciding in System 1 & 2 supervene on activity in the body, especially the nervous system. There is no reason to think that the idea of a “will” making decisions, either nonconsciously or consciously, is incompatible with a naturalistic worldview. Having a System 2 type decision making ability justifies the continuation of our current social practices of holding people responsible for their consciously chosen actions. But the recognition of the importance of System 1 for influencing the supposedly “free” System 2 also forces us to recognize that people are not responsible for everything they think, perceive, feel, and do. We do not hold someone accountable for what they do if we know they are sleepwalking. System 2 must be activated if we are going to hold someone accountable to abstract moral principles, since it is only System 2 that takes such principles into consideration when deciding what to do. It is up to the theist to show that these naturalistic models of the will are incoherent or talking about the wrong thing. Although many theists will simply say “System 2” is not what they are referring to when they talk about free will. But I think this is simply bad phenomenology. The phenomenal features of System 2 are pretty much exactly the same as those of free will, commonly understood. It is only on account of the presupposition that God exists that theists conclude the will must be free from physical constraints. But any scientifically literate person knows that this can’t be true. The will is fundamentally embodied, and thus constrained and not free.
- Cosmological argument. It is claimed by theists that the universe must have had a beginning since the idea of an actual infinite chain of universes is incoherent. But is it? As many atheists have pointed out, if theists can imagine an endless future (Heaven), they should be able to imagine an beginningless past. And if a beginningless past is conceivable, we have good reason to think it is possible. And if it is possible, the idea that God must necessarily exist in order to create the universe we find ourselves in goes out the window. For it is equally possible to suppose that God didn’t create the universe, and that this universe was simply preceded by another universe, and that universe was preceded by another universe, and so on. It seems possible to simply respond to the cosmological argument by saying in it’s equally possible that the natural cosmos has always existed in one form or another. Theists claim that the multiverse is an ad hoc hypothesis that cannot be empirically verified. But so is the God hypothesis. And even if we were to accept that the universe was intelligently created, we need not suppose that a monotheistic deity (God) did the creation. It is conceivable (and therefore possible) that a whole TEAM of creators created the universe. This is, of course, Hume’s reply. Even if all the evidence points says that our particular universe was created (which it doesn’t), we have no reason to believe that God created it. It might have been created by a team of advanced aliens who figured out how to create universes by collasping blackholes or something. Or if we went with the supernatural hypothesis, we can suppose that our universe was created by a legion of different gods instead of just one omniGod.Modern theists like to imagine that omniGod is the only conceivable form a supernatural realm could take on. But more than one god existing is just as conceivable as just one god existing. And modern readings of the Bible support the idea that the Hebrews were once polytheists but slowly transitioned into monotheists.
- Fine tuning. The idea that the physical constants of the universe are “fine tuned” to support life is not a knockdown argument for God’s existence. The apparent fine-tuning of the physical constants to support life here on Earth is compatible with the weak anthropic principle. The weak anthropic principle simply states that “The conditions observed must support the existence of the observer”. That is to say, if the conditions were not fine-tuned to support life on Earth, we could not be here to remark on the fact that the conditions around us seem fine-tuned to support our existence. And we have no empirical reason to believe that our form of life is the only possible form of life. So although the fine-tuning argument for God’s existence rightly points out some limitations of our current understanding of the cosmos, it is by no means a knock-down argument since there are possible naturalistic explanations for why it appears that the universe is fine-tuned for existence. Since we can imagine at least one possible naturalistic explanation for why the conditions observed are the way they are (the alien technology possibility, which is compatible with the beginningless past possibility), the fine-tuning argument for God’s existence loses it “necessary” oomph. It just becomes one more possibility among others than we can contemplate.
- Personal experience. This is the ultimate trump card for most intellectually sophisticated theological apologists. They claim that belief in God is properly basic in the sense that it isn’t believed on the basis of some evidence or argument, but is directly believed in virtue of immediate experience of God. Theologians claim to have direct subjective evidence for the reality of God based on their experience. The experiences are usually either a peak or mystical experience or an experience where something amazing happens to you (perhaps in response to a prayer or a faith healer praying on your behalf). While it is probably true that there is no way to argue against that fact that someone claims they had this experience, this is no reason to believe God really exists. It’s part of the language game that we have to accept the subjective testimony of rational adults (and there is no question that theologians are by and large capable of thinking rationally). So if someone claims to have directly experienced the divine realm, or who claims to have been touched by God, what recourse does a naturalistic atheist have against these claims? None. But this isn’t a win for the theist since if this is the game played, then apologetics is dead since at this point the theist gives up on trying to convince atheists that God exists, and instead only try to argue that they are rational in believing what they believe. But since “it is true since I experienced it as true” is not a good way to convince a skeptic that a claim is true, the atheist is not going to convert to theism on account of a report of subjective experience of God, since there are many other more plausible explanations, such as that the person who claims to have experienced God was simply hallucinating, or experienced an altered state of consciousness in response to either internal or external perturbations. So while the atheist cannot claim that the theist is irrational in using his experience as the basis for the claim that God is properly basic, this cannot convince the skeptic (nor can it convince other religious people like Mormons, Jews, or Muslims). For good reason. People claim to have experienced all sorts of wild things, such as that they were abducted by aliens, or that they can really astral project, or in any number of occult, paranormal, or superstitious reports. Humans are still recovering from their primitive and superstitious past. There is good evidence that religious experiences generated by the brain were an exaptation that allowed for the growth of civilization in the Neolithic era. We thus have a naturalistic explanation of why people report religious experience and why they are so certain in the truth of their claims. The atheist is not convinced by those claims because the alternate explanation that religious experience strongly supervenes on nervous and bodily states triggered by internal and external stimuli is much more plausible in light of his methodological and metaphysical convictions.
There is much more I could say in favor of the cumulative case for naturalistic atheism. What I have written here only counts as a fraction of all the evidence and philosophical reasoning in support of naturalism and atheism. There is a huge atheistic literature that I think is overwhelmingly convincing in its argumentation and reasoning (see the “Debunking Christianity” blog by John Loftus in the blogroll side bar to the right). I have seen every positive argument for God refuted over and over. For this reason most theists resort to personal experience as the ultimate epistemological trump card and simply give up on trying to convert the skeptic. They simply want to live in peace and practice their religion and indoctrinate their children such that they too believe the religious claims. This is fine, but I think it significantly weakens the case for theism to allow personal experience to trump skeptical requests for positive argumentation and empirical evidence for their beliefs, particularly if we think that we have a moral obligation to teach our children the truth.