Atheism, in general, the critique and denial of metaphysical beliefs in God or spiritual beings. As such, it is usually distinguished from theism, which affirms the reality of the divine and often seeks to demonstrate its existence. Atheism is also distinguished from agnosticism, which leaves open the question whether there is a god or not, professing to find the questions unanswered or unanswerable.

The dialectic of the argument between forms of belief and unbelief raises questions concerning the most perspicuous delineation, or characterization, of atheism, agnosticism, and theism. It is necessary not only to probe the warrant for atheism but also carefully to consider what is the most adequate definition of atheism. This article will start with what have been some widely accepted, but still in various ways mistaken or misleading, definitions of atheism and move to more adequate formulations that better capture the full range of atheist thought and more clearly separate unbelief from belief and atheism from agnosticism. In the course of this delineation the section also will consider key arguments for and against atheism.

A central, common core of Judaism, Christianity, and Islam is the affirmation of the reality of one, and only one, God. Adherents of these faiths believe that there is a God who created the universe out of nothing and who has absolute sovereignty over all his creation; this includes, of course, human beingswho are not only utterly dependent on this creative power but also sinful and who, or so the faithful must believe, can only make adequate sense of their lives by accepting, without question, Gods ordinances for them. The varieties of atheism are numerous, but all atheists reject such a set of beliefs.

Atheism, however, casts a wider net and rejects all belief in spiritual beings, and to the extent that belief in spiritual beings is definitive of what it means for a system to be religious, atheism rejects religion. So atheism is not only a rejection of the central conceptions of Judaism, Christianity, and Islam; it is, as well, a rejection of the religious beliefs of such African religions as that of the Dinka and the Nuer, of the anthropomorphic gods of classical Greece and Rome, and of the transcendental conceptions of Hinduism and Buddhism. Generally atheism is a denial of God or of the gods, and if religion is defined in terms of belief in spiritual beings, then atheism is the rejection of all religious belief.

It is necessary, however, if a tolerably adequate understanding of atheism is to be achieved, to give a reading to rejection of religious belief and to come to realize how the characterization of atheism as the denial of God or the gods is inadequate.

To say that atheism is the denial of God or the gods and that it is the opposite of theism, a system of belief that affirms the reality of God and seeks to demonstrate his existence, is inadequate in a number of ways. First, not all theologians who regard themselves as defenders of the Christian faith or of Judaism or Islam regard themselves as defenders of theism. The influential 20th-century Protestant theologian Paul Tillich, for example, regards the God of theism as an idol and refuses to construe God as a being, even a supreme being, among beings or as an infinite being above finite beings. God, for him, is being-itself, the ground of being and meaning. The particulars of Tillichs view are in certain ways idiosyncratic, as well as being obscure and problematic, but they have been influential; and his rejection of theism, while retaining a belief in God, is not eccentric in contemporary theology, though it may very well affront the plain believer.

Second, and more important, it is not the case that all theists seek to demonstrate or even in any way rationally to establish the existence of God. Many theists regard such a demonstration as impossible, and fideistic believers (e.g., Johann Hamann and Sren Kierkegaard) regard such a demonstration, even if it were possible, as undesirable, for in their view it would undermine faith. If it could be proved, or known for certain, that God exists, people would not be in a position to accept him as their sovereign Lord humbly on faith with all the risks that entails. There are theologians who have argued that for genuine faith to be possible God must necessarily be a hidden God, the mysterious ultimate reality, whose existence and authority must be accepted simply on faith. This fideistic view has not, of course, gone without challenge from inside the major faiths, but it is of sufficient importance to make the above characterization of atheism inadequate.

Finally, and most important, not all denials of God are denials of his existence. Believers sometimes deny God while not being at all in a state of doubt that God exists. They either willfully reject what they take to be his authority by not acting in accordance with what they take to be his will, or else they simply live their lives as if God did not exist. In this important way they deny him. Such deniers are not atheists (unless we wish, misleadingly, to call them practical atheists). They are not even agnostics. They do not question that God exists; they deny him in other ways. An atheist denies the existence of God. As it is frequently said, atheists believe that it is false that God exists, or that Gods existence is a speculative hypothesis of an extremely low order of probability.

Yet it remains the case that such a characterization of atheism is inadequate in other ways. For one it is too narrow. There are atheists who believe that the very concept of God, at least in developed and less anthropomorphic forms of Judeo-Christianity and Islam, is so incoherent that certain central religious claims, such as God is my creator to whom everything is owed, are not genuine truth-claims; i.e., the claims could not be either true or false. Believers hold that such religious propositions are true, some atheists believe that they are false, and there are agnostics who cannot make up their minds whether to believe that they are true or false. (Agnostics think that the propositions are one or the other but believe that it is not possible to determine which.) But all three are mistaken, some atheists argue, for such putative truth-claims are not sufficiently intelligible to be genuine truth-claims that are either true or false. In reality there is nothing in them to be believed or disbelieved, though there is for the believer the powerful and humanly comforting illusion that there is. Such an atheism, it should be added, rooted for some conceptions of God in considerations about intelligibility and what it makes sense to say, has been strongly resisted by some pragmatists and logical empiricists.

While the above considerations about atheism and intelligibility show the second characterization of atheism to be too narrow, it is also the case that this characterization is in a way too broad. For there are fideistic believers, who quite unequivocally believe that when looked at objectively the proposition that God exists has a very low probability weight. They believe in God not because it is probable that he existsthey think it more probable that he does notbut because belief is thought by them to be necessary to make sense of human life. The second characterization of atheism does not distinguish a fideistic believer (a Blaise Pascal or a Soren Kierkegaard) or an agnostic (a T.H. Huxley or a Sir Leslie Stephen) from an atheist such as Baron dHolbach. All believe that there is a God and God protects humankind, however emotionally important they may be, are speculative hypotheses of an extremely low order of probability. But this, since it does not distinguish believers from nonbelievers and does not distinguish agnostics from atheists, cannot be an adequate characterization of atheism.

It may be retorted that to avoid apriorism and dogmatic atheism the existence of God should be regarded as a hypothesis. There are no ontological (purely a priori) proofs or disproofs of Gods existence. It is not reasonable to rule in advance that it makes no sense to say that God exists. What the atheist can reasonably claim is that there is no evidence that there is a God, and against that background he may very well be justified in asserting that there is no God. It has been argued, however, that it is simply dogmatic for an atheist to assert that no possible evidence could ever give one grounds for believing in God. Instead, atheists should justify their unbelief by showing (if they can) how the assertion is well-taken that there is no evidence that would warrant a belief in God. If atheism is justified, the atheist will have shown that in fact there is no adequate evidence for the belief that God exists, but it should not be part of his task to try to show that there could not be any evidence for the existence of God. If the atheist could somehow survive the death of his present body (assuming that such talk makes sense) and come, much to his surprise, to stand in the presence of God, his answer should be, Oh! Lord, you didnt give me enough evidence! He would have been mistaken, and realize that he had been mistaken, in his judgment that God did not exist. Still, he would not have been unjustified, in the light of the evidence available to him during his earthly life, in believing as he did. Not having any such postmortem experiences of the presence of God (assuming that he could have them), what he should say, as things stand and in the face of the evidence he actually has and is likely to be able to get, is that it is false that God exists. (Every time one legitimately asserts that a proposition is false one need not be certain that it is false. Knowing with certainty is not a pleonasm.) The claim is that this tentative posture is the reasonable position for the atheist to take.

An atheist who argues in this manner may also make a distinctive burden-of-proof argument. Given that God (if there is one) is by definition a very recherch realitya reality that must be (for there to be such a reality) transcendent to the worldthe burden of proof is not on the atheist to give grounds for believing that there is no reality of that order. Rather, the burden of proof is on the believer to give some evidence for Gods existencei.e., that there is such a reality. Given what God must be, if there is a God, the theist needs to present the evidence, for such a very strange reality. He needs to show that there is more in the world than is disclosed by common experience. The empirical method, and the empirical method alone, such an atheist asserts, affords a reliable method for establishing what is in fact the case. To the claim of the theist that there are in addition to varieties of empirical facts spiritual facts or transcendent facts, such as it being the case that there is a supernatural, self-existent, eternal power, the atheist can assert that such facts have not been shown.

It will, however, be argued by such atheists, against what they take to be dogmatic aprioristic atheists, that the atheist should be a fallibilist and remain open-minded about what the future may bring. There may, after all, be such transcendent facts, such metaphysical realities. It is not that such a fallibilistic atheist is really an agnostic who believes that he is not justified in either asserting that God exists or denying that he exists and that what he must reasonably do is suspend belief. On the contrary, such an atheist believes that he has very good grounds indeed, as things stand, for denying the existence of God. But he will, on the second conceptualization of what it is to be an atheist, not deny that things could be otherwise and that, if they were, he would be justified in believing in God or at least would no longer be justified in asserting that it is false that there is a God. Using reliable empirical techniques, proven methods for establishing matters of fact, the fallibilistic atheist has found nothing in the universe to make a belief that God exists justifiable or even, everything considered, the most rational option of the various options. He therefore draws the atheistical conclusion (also keeping in mind his burden-of-proof argument) that God does not exist. But he does not dogmatically in a priori fashion deny the existence of God. He remains a thorough and consistent fallibilist.

Such a form of atheism (the atheism of those pragmatists who are also naturalistic humanists), though less inadequate than the first formation of atheism, is still inadequate. God in developed forms of Judaism, Christianity, and Islam is not, like Zeus or Odin, construed in a relatively plain anthropomorphic way. Nothing that could count as God in such religions could possibly be observed, literally encountered, or detected in the universe. God, in such a conception, is utterly transcendent to the world; he is conceived of as pure spirit, an infinite individual who created the universe out of nothing and who is distinct from the universe. Such a realitya reality that is taken to be an ultimate mysterycould not be identified as objects or processes in the universe can be identified. There can be no pointing at or to God, no ostensive teaching of God, to show what is meant. The word God can only be taught intralinguistically. God is taught to someone who does not understand what the word means by the use of descriptions such as the maker of the universe, the eternal, utterly independent being upon whom all other beings depend, the first cause, the sole ultimate reality, or a self-caused being. For someone who does not understand such descriptions, there can be no understanding of the concept of God. But the key terms of such descriptions are themselves no more capable of ostensive definition (of having their referents pointed out) than is God, where that term is not, like Zeus, construed anthropomorphically. (That does not mean that anyone has actually pointed to Zeus or observed Zeus but that one knows what it would be like to do so.)

In coming to understand what is meant by God in such discourses, it must be understood that God, whatever else he is, is a being that could not possibly be seen or be in any way else observed. He could not be anything material or empirical, and he is said by believers to be an intractable mystery. A nonmysterious God would not be the God of Judaism, Christianity, and Islam.

This, in effect, makes it a mistake to claim that the existence of God can rightly be treated as a hypothesis and makes it a mistake to claim that, by the use of the experimental method or some other determinate empirical method, the existence of God can be confirmed or disconfirmed as can the existence of an empirical reality. The retort made by some atheists, who also like pragmatists remain thoroughgoing fallibilists, is that such a proposed way of coming to know, or failing to come to know, God makes no sense for anyone who understands what kind of reality God is supposed to be. Anything whose existence could be so verified would not be the God of Judeo-Christianity. God could not be a reality whose presence is even faintly adumbrated in experience, for anything that could even count as the God of Judeo-Christianity must be transcendent to the world. Anything that could actually be encountered or experienced could not be God.

At the very heart of a religion such as Christianity there stands a metaphysical belief in a reality that is alleged to transcend the empirical world. It is the metaphysical belief that there is an eternal, ever-present creative source and sustainer of the universe. The problem is how it is possible to know or reasonably believe that such a reality exists or even to understand what such talk is about.

It is not that God is like a theoretical entity in physics such as a proton or a neutrino. They are, where they are construed as realities rather than as heuristically useful conceptual fictions, thought to be part of the actual furniture of the universe. They are not said to be transcendent to the universe, but rather are invisible entities in the universe logically on a par with specks of dust and grains of sand, only much, much smaller. They are on the same continuum; they are not a different kind of reality. It is only the case that they, as a matter of fact, cannot be seen. Indeed no one has an understanding of what it would be like to see a proton or a neutrinoin that way they are like Godand no provision is made in physical theory for seeing them. Still, there is no logical ban on seeing them as there is on seeing God. They are among the things in the universe, and thus, though they are invisible, they can be postulated as causes of things that are seen. Since this is so it becomes at least logically possible indirectly to verify by empirical methods the existence of such realities. It is also the case that there is no logical ban on establishing what is necessary to establish a causal connection, namely a constant conjunction of two discrete empirical realities. But no such constant conjunction can be established or even intelligibly asserted between God and the universe, and thus the existence of God is not even indirectly verifiable. God is not a discrete empirical thing or being, and the universe is not a gigantic thing or process over and above the things and processes in the universe of which it makes sense to say that the universe has or had a cause. But then there is no way, directly or indirectly, that even the probability that there is a God could be empirically established.

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Atheism - Britannica.com