First, we have to define a few terms, albeit not with extreme philosophical rigor. Not only would that be tedious and boring, it would ineffective: our aim is not to determine whether the proposition is true or false in some technical sense, but in a broad and general sense, a pragmatic and useful understanding. Thus we should keep our definitions general and pragmatic, because our intended audience is the world of the practical and applicable.

With that in mind, we can define rational in a rough and ready sense, as "within the rules of reason." Those rules include the Aristotelian laws of logic (Identity, Negation, and Excluded Middle) and the principle of Parsimony (also called Occam's Razor).

The laws of logic aren't terribly important here; we can sum them up as the idea that a thing is itself, it is not it’s negation, and it is either itself or not, but nothing in between.

Occam's Razor perhaps needs more explanation, since it is often misunderstood. Originally formulated as "do not multiply entities needlessly," it is often mischaracterized as a rule of simplicity, or sometimes as an abstract and infrequently used principle. Since my argument will depend heavily on parsimony, allow me to illustrate what it is, and how ordinary people use it in ordinary logic every day, through an example.

Suppose I come to you with a theory that rain is caused by evaporation, condensation, and an invisible elf. Through much mathematics and experiment, you manage to show that the invisible elf is not necessary or useful to the theory, and thus adds no explanatory power to the normal theory of evaporation and condensation.

Then suppose I suggest a new theory: evaporation, condensation, and two invisible elves. Again you show that two elves are no better than one, which is no better than none. Now I suggest three elves, and at this point you throw up your hands and exclaim, "It doesn't matter how many invisible elves you add. They're all indistinguishable from no elf at all!" At that point you have just invoked parsimony, asserting that by the rules of reason, any theory that is indistinguishable from another one save for the existence of irrelevant, un-testable entities is irrational.

This does not mean it is not true. It could be the case that an invisible elf is required to make rain, and we lack the ability to discern the hidden variables that would show this to be true. It could even be the case that the elf exists, and is necessarily undetectable by any and all means. It is possible for this state of affairs to be true; however, it is not rational for a person to assert it. One does not have an argument for that proposition that is constrained to the rules of reason.

There are probably a few other principles that constitute reason, but I don't think it is necessary to go to that depth. The above should be enough for our purposes here, and at a general enough level to still hold the interest of the practical world.

We should also say something about the nature of belief, chiefly to distinguish from its close and often confused cousin, hope. Again, a simple example:

If you buy a lottery ticket, you are entitled to hope that you will win. You can dream about the things you'll buy, and even share your dreams with your friends. You can take pleasure and comfort in those dreams.

But you are not entitled to believe that you will win; if you quit your job and make a down-payment on a yacht, no one will hesitate to characterize you as irrational.

The atheist, in this example, is the person who won't even buy a ticket, preferring to spend his dollar on a candy bar and receive the immediate and concrete pleasure of a piece of chocolate to the fantasy of an infinite quantity of future chocolate. But since hope and pleasure are a matter of personal preference, neither the well-fed atheist nor the hopeful theist in this example are being irrational; the only crazy person is the one who thinks he's already won.

There are many definitions of this term, but we'll restrict ourselves to the classic Christian omni-max god; omnipotent, omniscient, and omni-benevolent. However, I think the following argument applies equally well to any disembodied personality or supernatural entity.

At this point I should make a disclaimer, if only to help clarify the position I am arguing from. I do not disbelieve in God because I am an atheist; rather, I disbelieve in God because I disbelieve in anything supernatural, and God is merely one of many alleged supernatural entities I disbelieve in. My position is called metaphysical naturalism, or sometimes strict materialism. It is possible to believe in the supernatural while rejecting the Christian God, but that is not my position, so I won't say anything more about it.

Indeed, one could extend my argument to say that it is irrational to believe in anything supernatural; and I would almost certainly agree with that extension.

The argument is quite simple: there is no evidence for the existence of God. (As La'Place said, "Sir, I have no need of that hypothesis.") What I mean by this is exactly the same thing you meant in the argument above when you said there was no evidence for the existence of invisible rain-causing elves: that entity adds no explanatory power. The existence of the world minus God is indistinguishable from the existence of the world plus God. Once this is stipulated, the principle of parsimony makes it clear that it is irrational to believe in God.

Thus, the only possible rebuttal is to present evidence of God. In anticipation of that, I will dispense with a few of the more common claims.

Sometimes it is claimed that morality is not possible without God; or even that the concepts of good and evil are only meaningful when defined with respect to God. The rebuttal of this evidence is painfully easy: Japan (as just one example). No one can claim that classical Japan (that is, before any possible introduction of Christian belief) was not concerned with morality, or ignorant of good and evil. It might not be the same moral code as the Christian one; but they clearly had a moral code, made distinctions between justice and injustice, railed against evil and strived to do good. Thus, it is empirically evident that a society can be orderly, polite, and morally constrained, even in the absence of any notion of the Christian God.

One might argue that classical Japan owed its notion of morality to God anyway, having derived it from Him unknowingly; for instance, you could argue that the very nature of Man, being in God's image and sharing in the fruit of the tree of Knowledge, necessarily constructs morality even in the absence of conscious knowledge of God. But this argument fails to parsimony; once you have asserted that morality is a natural product of human nature (as indeed I do), what does God have to offer this theory? At what point in a person's life does God act or not act to make them moral? None, of course: the machinery produces morality on its own. God as a component of moral development is unnecessary. The best you can do is claim that God designed Man this way, which leads us to the next general body of claims.

A powerful argument for the supernatural used to be the mystery of consciousness. It was hard to assert that everything was material when we had no clue how something as abstract and immaterial as consciousness could derive from the material. The abstract nature of morality is really just a special case of this general claim: how can personality derive from the non-personal? Thus God, or at least the supernatural, must be the source of the personal.

The answer is simple: it's a neat trick. Again, allow me to illustrate by example.

When I was in college studying philosophy (many, many years ago), I remember all the rage was over definitions. People could identify a horse, even while philosophers could not construct a method or set of rules for identifying horses. The smartest scholars would labor for months to construct long sets of rules regarding what constitutes a horse. Then some wag would take a horse, cut off its legs and paint it blue. Now the definition failed on page 29; but any four-year-old could still easily and readily identify the object as a horse. "I think it's a horse," she would say, "even though you cut off its legs and painted it blue to disguise it."

And then some particularly gifted wag invented "neural networks," a series of mathematical equations you could instantiate on a computer. First show the computer hundreds of pictures of horses, in various situations and breeds. Then show it a picture of a blue horse with no legs. The machine would whir for a while, and finally come back with the mechanical equivalent of: "I think it's a horse." It turned out that all that sturm and drang over definitions was wasted: in the end, they were just a clever mathematical trick.

Our brains apparently store faces as Eigen values, as coordinates in a mathematical space. One consequence of this is that we can record many faces with few data points; another is that asymmetric faces are foreign when viewed in a mirror (you readily recognize human faces in a mirror, because they are so symmetric; but try looking at your tuxedo cat's face in the mirror – it takes you a second to realize that it's your cat). Another consequence is that all Orientals really do look alike to Westerners, and vice versa; the mathematical map in your head is heavily weighted to the tiny differences of features you've grown up with. Japanese people can tell the difference between Koreans, Chinese, and Thais as easily as you can tell the difference between French, Norwegian, and Italian. Again, the product of a clever mathematical trick.

Without going into exhaustive detail, the general consensus of neurological research today is that consciousness is also just a clever mathematical trick. We know this because messing with the hardware messes with the mind; there are people with damaged brains that cannot tell the difference between faces, or identify horses even when they aren't painted blue (and yet, some of those people can still ride a horse even while they can't name the beast).

So consciousness turns out to rely solely on the brain; again we find that the supernatural is not necessary to explain the ordinary day-to-day functioning of our minds, including morality (which is just the product of our social existence and theory of mind, or the idea that we can imagine being in the other guy's shoes). And again God is forced out by parsimony to some earlier stage; perhaps God created existence itself.

At this point the argument does change a bit. The physicists present an argument explaining how something came from nothing, but perhaps you don't find it compelling: it is, after all, a fairly abstract and tenuous argument.

But that doesn't help the case for God at all. Merely asserting, or even proving, that the universe required some uncaused cause does not lead you to the Christian God. You might defeat parsimony by showing that something originally had to construct our space-time; but there is no possible way to show that something is a personal being who is concerned with good, evil, or the conduct of man. Or even that the original casual agent still exists. A simple acorn produces a gloriously complex tree; but the acorn does not rule the tree, judge its fate, or even still exist. Who is to say that the original cause was not consumed in the birth of the universe? It is possible it was not, but it is also possible that it was.

What you need is some way of distinguishing between these possible states of affairs; otherwise, parsimony executes the existence of an entity that has no discernible effect on the affairs of the world today. Physics cannot yet give you that method; they claim that all they need to get things started is a single tiny particle; just one nameless, faceless, electron is enough, a perfectly ordinary electron indistinguishable from all others save that it has no obvious material casual history. And it doesn't even have to exist anymore.

So you need a way to find out information that merely observing the natural world cannot (at this time) give you. Which leads us to the last category of evidence.

This is the final argument, then: I know of God because God revealed himself to me. On the surface, it seems to be the perfect fit: your personal knowledge is evidence, a way to distinguish between sets of affairs that otherwise look the same.

But this is the same as asking if we can explain the existence of your personal knowledge, while still confining ourselves to the material world. The answer now becomes rather obvious: perhaps you're wrong. After all, we all have a wealth of evidence that our personal knowledge can sometimes be just plain wrong.

We also have a method for determining whether our personal experience is reliable or not. Sometimes called the scientific method, empiricism, or often just common sense; what we do is determine if the knowledge in question is in our heads, or in the world. We do this by recourse to another person's point of view. If I see an elephant in the living room, I ask other people if they see one. Or I take a picture. Or I get a photon detector and see if it can register a lamp held on the other side of the elephant.

Which leads us to the rebuttal of personal revelation; namely, that there are as many revelations of God as there are religious worshippers (more, actually, since some people have new revelations and change their minds). All attempts to objectify or quantify these revelations fail to converge to a single point. In the above example, suppose the other person in the room doesn't even know what an elephant is. How then can they confirm its presence or non-presence in the room? Well, I could go stand behind the elephant and ask them: can you still see me? If they say no, then there's a clue that something is there; but if they say yes, of course, then the best I can do is make sure they aren't lying. "How many fingers am I holding up?" I ask, and when they get it right ten times in a row, I have to conclude: nothing is blocking their vision. They certainly don't see anything in the way.

Unless it's a transparent elephant – but now we are redefining our original claim. If we are allowed to constantly redefine our claim, we will eventually wind up with an entity whose existence is indistinguishable from its non-existence; and then of course, comes parsimony with the axe.

It is not just the sheer diversity of personal revelation that proves it is unreliable; it is their inability to converge to a single point. Physicists study various phenomena, and constantly refine them to a single explanation; indeed, that is the very definition of "progress" in physics. Math, medicine, car mechanics, all other disciplines also resort to empirical methods to produce singular truths from multiple hypothesis; the fact that religion alone cannot do this is compelling evidence that there is nothing there to converge on. I say compelling, because in every other case save religion, this inability to converge is taken as proof: each of us has, at one time or another, applied this method to correct our own failures of perception.

That people make mistakes is incontrovertible; that they occasionally commit to false conclusions undeniable. A method for distinguishing between our facts and our fancies has been applied since we invented language, and there's no reason to think it shouldn't be applied to a particular set of claims. The private imaginations of our minds are no source of knowledge about God, anymore than imagination about the accused criminal in the docket is a rational source of knowledge about his guilt or innocence.

What we have shown, then, is that in the absence of evidence, it is irrational to believe. Anything, really; God is merely one object that it is irrational to assert the existence of without evidence for. The standard atheist argument for this can be summed up in one sentence: "Explain to me why you don't believe in Zeus, and then I'll explain to you why I don't believe in God." Or, as has been said, "We're all atheists here; you just disbelieve in one fewer God than I do." People generally reject tales of Zeus and the Easter Bunny as fiction, precisely because they fail to confine themselves to the rules of reason: that is, they lack evidence that cannot be explained by recourse to fewer entities and simpler explanations. Why wouldn't God be in the same basket?

This does not mean God is not true; nor does it mean we will never prove that God is or is not true. It merely means that it is irrational to commit to a belief for which you have no evidence. Lacking evidence, and here we mean real evidence, the kind that cannot be explained by recourse to fewer entities and simpler explanations, belief in God is irrational.

Micheal Planck

Words: 3000 approx