After millennia of trying to come up with arguments for the existence of God, all theologians and philosophers have been able to produce are lame logical fallacies. No credible evidence has ever been found for the existence of a god. Of course, it is impossible to prove conclusively that gods don't exist just like its impossible to conclusively prove that Santa Claus, the Easter Bunny, and the Invisible Pink Unicorn don't exist. However, it is irrational to believe in fanciful creatures for which there is no evidence. As Carl Sagan said,

"Extraordinary claims require extraordinary evidence."

Not only are there no sound arguments indicating that a god exists, there are several sound arguments indicating that God does not exist. This article introduces some of these arguments and provides links to other articles which discuss the arguments more thoroughly.

The fact that there is no valid reason to believe that a god exists justifies weak atheism (lack of belief in gods), but not strong atheism (belief that there are no gods). Lack of evidence for a proposition ("God exists" in this case) is, in and of itself, not evidence that the proposition is false. However, lack of evidence for a proposition combined with the expectation that if that proposition were true that evidence would be available does constitute evidence that the proposition is false. As an example of this reasoning, suppose someone claimed that there is a herd of invisible two-ton elephants stampeding through your living room. If such a claim were true there would be plenty of evidence in the form of broken furniture for example. Now you examine your living room and find no evidence for stampeding elephants. It is, of course, rational to believe that the elephant claim was false. Now lets consider the gods of the dominate theistic religions: Judaism, Christianity, and Islam. Each of these religions postulate a god that is concerned with human welfare and that performs miracles. If such a god exists, there should be ample evidence of the miracles that he works whenever human suffering is present. But human suffering certainly exists and there is no evidence of the theists' god. This constitutes evidence that this god does not exist.

The Argument from Evil is thousands of years old, going back at least to the ancient Greek philosopher Epicurus, who argued that the existence of evil is logically incompatible with the existence of a being with the properties usually attributed to a god. Epicurus' version of the argument neglects to consider the possibility that some evil could coexist with a god if the god has some higher moral purpose that requires the evil to exist. The modern version of the argument avoids this objection by taking as its main premise the observation that evil and human suffering exists that is not necessary for some greater good. This premise can be justified by noting that any necessary level of evil in the world can be satisfied by moral evil, which is defined as evil that is the result of human action. Therefore, natural evil, which results from natural occurrences such as natural disasters, is gratuitous.

The modern version of the Argument from Evil can be stated as follows: If the theists' version of god exists, then he is by definition a being who is omnipotent, omniscient, and benevolent. Since this god is benevolent, he would want to eliminate all evil and human suffering that is not necessary for some higher moral purpose; and since this god is omnipotent, he should be easily able to do so. But unnecessary evil and human suffering do exist. Therefore, the theists' version of god does not exist.

A common modification of the argument is to replace the premise "unnecessary evil and human suffering exists" with "evil and human suffering exists that is in all probability unnecessary". The conclusion is then modified to "God most probably does not exist." The argument is then not a logical proof of the nonexistence of God, but a demonstration that apparently gratuitous evil is evidence for the nonexistence of God. (Other arguments in this article that are presented as deductive arguments can also be interpreted as evidential arguments).

A standard attempt to rebut the argument is to claim that the apparently gratuitous evil that we observe is, in fact, necessary to God's purpose. These rebuttals are called theodicies. The most commonly used theodicy is the Free Will Defense, which argues that God must allow some evil to exist, since he gives humans free will and therefore allows people to sin. This may be a reasonable rebuttal to Epicurus' argument, but it really does not apply to the modern version of the Argument from Evil, since not all evil is the result of free will. Other theodicies have been proposed, but they are very strained and totally unconvincing. There is no reasonable theodicy that can excuse a being capable of preventing the natural disasters that kill so many people every year from not doing so.

Jeffery Jay Lowder argued in the March 1999 newsletter of the Internet Infidels that a case for metaphysical naturalism can be made from the Argument from Evil and the Argument from Physical Minds. Here is the latter argument:

As Paul Draper, an agnostic philosopher at Florida International University, puts it, "Consciousness and personality are highly dependent on the brain. Nothing mental happens without something physical happening." Now Michael Tooley, a philosopher at the University of Colorado at Boulder, has stated five lines of evidence in support of this claim. Let me summarize just briefly that evidence. First, when an individuals brain is directly stimulated and put into a certain physical state, this causes the person to have a corresponding experience. Second, certain injuries to the brain make it impossible for a person to have any mental states at all. Third, other injuries to the brain destroy various mental capacities. Which capacity is destroyed is tied directly to the particular region of the brain that was damaged. Fourth, when we examine the mental capacities of animals, they become more complex as their brains become more complex. And fifth, within any given species, the development of mental capacities is correlated with the development of neurons in the brain. Thus, the conclusion that, "Nothing mental happens without something physical happening," seems inescapable.

But if nothing mental happens without something physical happening, that strongly implies that the mind cannot exist independently of physical arrangements of matter. In other words, we do not have a soul. And this is exactly what we would expect if naturalism is true. But if theism is true, then our minds should not depend on our brains for their existence; we should have souls. Also, if theism is true, then God is a disembodied mind; Gods mind is not in any sense dependent on physical arrangements of matter. But if nothing mental happens without something physical happening, that is evidence against both the existence of souls and the existence of any being who is supposed to have a disembodied mind, including God. Therefore, the physical nature of minds is unlikely if theism is true, but what we would expect if naturalism is true.

Another reason for believing that the theists' version of god does not exist is the Argument from Nonbelief which goes as follows: The theists' god is a benevolent god who rewards believers and damns nonbelievers; such a god would want everyone to be a believer. Since this god is also omnipotent, he should easily be able to convince nonbelievers to believe. It then follows that if the theists' version of god exists, there would not be any nonbelievers. There are, however, many nonbelievers in the world. Therefore, this god does not exist.

A recently proposed atheological argument is the Moral-Knowledge Argument, which can be expressed as follows: If the theists' version of god exists, then he is a being who is omnipotent, omniscient, and benevolent. Since this god is benevolent and his ethics are supposedly morally good for humanity, he would want all human beings to know his ethics perfectly. And since this god is omnipotent, it would be within his capacity to make sure that all human beings know his ethics perfectly. However, all human beings do not know his ethics perfectly, which is shown by their disagreeing about many moral values. Therefore, this version of god does not exist.

What about a more generic god? Suppose that there is a conscious god that created the universe and now just stands back and watches his creation without ever interfering with it. Ockham's Razor (don't postulate the existence of anything more than what's needed for explanation) certainly justifies weak atheism in this case. The basic idea behind Ockham's Razor can be used to justify belief in the nonexistence of this god as well. Since we cannot know for certain how the universe was created or even if it was created, the best we can do is decide if some of the many possible scenarios are more likely than others. Applying the idea of Ockham's Razor, we have to conclude that the scenarios that involve a more complex explanation for the universe are more unlikely than the scenarios with a simpler explanation. Since explanations that invoke a conscious god include an extremely complex being and naturalistic explanations do not, we can conclude that the scenarios involving a god are much less likely than scenarios that do not. Therefore a tentative belief that this generic god does not exist is justified. For a more thorough examination of this type of argument, see Science, Complexity, and God.

Another class of atheological arguments are the incompatible-properties arguments, which argue that God, as defined by theists, has mutually contradictory properties and therefore cannot exist. These incompatible-properties arguments are probably best understood as proof that theists don't know what they are talking about when they describe their god, rather than proof that God does not exist.

In conclusion, weak atheism is the default position. If there were no evidence for the existence or nonexistence of gods, weak atheism would be the only rational position to take. In order to move from the default position of weak atheism to theism, a rational person would require credible evidence for the existence of a god. Similarly, to move from weak atheism to strong atheism, credible evidence for the nonexistence of gods would be required. Some freethinkers find that the evidence that gods do not exist is convincing and that strong atheism is justified. Others think that the theists' description of their god is incoherent so that "God exists" is unintelligible and "not even wrong". Many atheists are also agnostics; even many strong atheists claim that the available evidence is sufficient to justify only a tentative belief in the nonexistence of gods and that actual knowledge is impossible. Finally, it should be noted that the position a person takes can vary depending on which version of god is being discussed.

For more arguments for the nonexistence of gods, see our Atheism Library.

If reason dictates that we should not believe in gods, then why do so many people still believe? One answer is memes. Another answer is close-mindedness. Many theists were brainwashed from birth to believe in their religion and they are simply not open-minded enough to ever seriously and honestly question their beliefs. Many freethinkers in the USA, on the other hand, were raised as theists but were open-minded enough to question what they were taught; the result is disbelief.