Atheism (Greek: a privative, and Theos, God, i.e. without God) is that system of thought which is formally opposed to theism. Since its first coming into use the term atheism has been very vaguely employed, generally as an epithet of accusation against any system that called in question the popular gods of the day. Thus, while Socrates was accused of atheism (Plato, Apol., 26 c.), and Diagoras called an atheist by Cicero (Nat. Deer., I, 23), Democritus and Epicurus were styled in the same sense impious (without respect for the gods) on account of the trend of their new atomistic philosophy. In this sense, too, the early Christians were known to the pagans as atheists, because they denied the heathen gods; while, from time to time, various religious opinions and philosophical systems have, for similar reasons, been deemed atheistic. Though atheism, historically considered, has meant no more in the past than a critical or sceptical denial of the theology of those who have employed the term as one of reproach, and has consequently no one strict philosophical meaning; though there is no one consistent system in the exposition of which it has a definite place; yet, if we consider it in its broad meaning as merely the opposite of theism, we shall be able to frame such divisions as will make possible a grouping of definite systems under this head. And in so doing we shall at once be adopting both the historical and the philosophical view. For the common basis of all systems of theism as well as the cardinal tenet of all popular religion at the present day is indubitably a belief in the existence of a personal God, and to deny this tenet is to invite the popular reproach of atheism. The need of some such definition as this was felt by Mr. Gladstone when he wrote (Contemporary Review, June, 1876): "By the Atheist I understand the man who not only holds off, like the sceptic, from the affirmative, but who drives himself, or is driven, to the negative assertion in regard to the whole unseen, or to the existence of God." Moreover, the breadth of comprehension in such a use of the term admits of divisions and cross-divisions being framed under it; and at the same time limits the number of systems of thought to which, with any propriety, it might otherwise be extended. Also, if the term is thus taken, in strict contradistinction to theism, and a plan of its possible modes of acceptance made, these systems of thought will naturally appear in clearer proportion and relationship.
Thus, defined as a doctrine, or theory, or philosophy formally opposed to theism, atheism can only signify the teaching of those schools, whether cosmological or moral, which do not include God either as a principle or as a conclusion of their reasoning. The most trenchant form which atheism could take would be the positive and dogmatic denial of the existence of any spiritual and extramundane First Cause. This is sometimes known as dogmatic, or positive theoretic, atheism; though it may be doubted whether such a system has ever been, or could ever possibly be seriously maintained. Certainly Bacon and Dr. Arnold voice the common judgment of thinking men when they express a doubt as to the existence of an atheist belonging to such a school. Still, there are certain advanced phases of materialistic philosophy that, perhaps, should rightly be included under this head. Materialism, which professes to find in matter its own cause and explanation, may go farther, and positively exclude the existence of any spiritual cause. That such a dogmatic assertion is both unreasonable and illogical needs no demonstration, for it is an inference not warranted by the facts nor justified by the laws of thought. But the fact that certain individuals have left the sphere of exact scientific observation for speculation, and have thus dogmatized negatively, calls for their inclusion in this specific type. Materialism is the one dogmatic explanation of the universe which could in any sense justify an atheistic position. But even materialism, however its advocates might dogmatize, could do no more than provide an inadequate theoretic basis for a negative form of atheism. Pantheism, which must not be confused with materialism, in some of its forms can be placed also in this division, as categorically denying the existence of a spiritual First Cause above or outside the world.
A second form in which atheism may be held and taught, as indeed it has been, is based either upon the lack of physical data for theism or upon the limited nature of the intelligence of man. This second form may be described as a negative theoretic atheism; and may be further viewed as cosmological or psychological, according as it is motived, on the one hand, by a consideration of the paucity of actual data available for the arguments proving the existence of a supersensible and spiritual God, or, what amounts to the same thing, the attributing of all cosmic change and development to the self-contained potentialities of an eternal matter; or, on the other hand, by an empiric or theoretic estimate of the powers of reason working upon the data furnished by sense-perception. From whichever cause this negative form of atheism proceeds, it issues in agnosticism or materialism; although the agnostic is, perhaps, better classed under this head than the materialist. For the former, professing a state of nescience, more properly belongs to a category under which those are placed who neglect, rather than explain, nature without a God. Moreover, the agnostic may be a theist, if he admits the existence of a being behind and beyond nature, even while he asserts that such a being is both unprovable and unknowable. The materialist belongs to this type so long as he merely neglects, and does not exclude from his system, the existence of God. So, too, does the positivist, regarding theological and metaphysical speculation as mere passing stages of thought through which the human mind has been journeying towards positive, or related empirical, knowledge. Indeed any system of thought or school of philosophy that simply omits the existence of God from the sum total of natural knowledge, whether the individual as a matter of fact believes in Him or not, can be classed in this division of atheism, in which, strictly speaking, no positive assertion or denial is made as to the ultimate fact of His being.
There are two systems of practical or moral atheism which call for attention. They are based upon the theoretic systems just expounded. One system of positive moral atheism, in which human actions would neither be right nor wrong, good nor evil, with reference to God, would naturally follow from the profession of positive theoretic atheism; and it is significant of those to whom such a form of theoretic atheism is sometimes attributed, that for the sanction of moral actions they introduce such abstract ideas as those of duty, the social instinct, or humanity. There seems to be no particular reason why they should have recourse to such sanctions, since the morality of an action can hardly be derived from its performance as a duty, which in turn can be called and known as a "duty" only because it refers to an action that is morally good. Indeed an analysis of the idea of duty leads to a refutation of the principle in whose support it is invoked, and points to the necessity of a theistic interpretation of nature for its own justification. The second system of negative practical or moral atheism may be referred to the second type of theoretic atheism. It is like the first in not relating human actions to an extramundane, spiritual, and personal lawgiver; not because such a lawgiver does not exist, but because the human intelligence is incapable of so relating them. It must not be forgotten, however, that either negative theoretic atheism or negative practical atheism is, as a system, strictly speaking compatible with belief in a God; and much confusion is often caused by the inaccurate use of the terms, belief, knowledge, opinion, etc.
Lastly, a third type is generally, though perhaps wrongly, included in moral atheism. "Practical atheism is not a kind of thought or opinion, but a mode of life" (R. Flint, Antitheistic Theories, Lect. I). This is more correctly called, as it is described, godlessness in conduct, quite irrespective of any theory of philosophy, or morals, or of religious faith. It will be noticed that, although we have included agnosticism, materialism, and pantheism, among the types of atheism, strictly speaking this latter does not necessarily include any one of the former. A man may be an agnostic simply, or an agnostic who is also an atheist. He may be a scientific materialist and no more, or he may combine atheism with his materialism. It does not necessarily follow, because the natural cognoscibility of a personal First Cause is denied, that His existence is called in question: nor, when matter is called upon to explain itself, that God is critically denied. On the other hand, pantheism, while destroying the extramundane character of God, does not necessarily deny the existence of a supreme entity, but rather affirms such as the sum of all existence and the cause of all phenomena whether of thought or of matter. Consequently, while it would be unjust to class agnostics, materialists, or pantheists as necessarily also atheists, it cannot be denied that atheism is clearly perceived to be implied in certain phases of all these systems. There are so many shades and gradations of thought by which one form of a philosophy merges into another, so much that is opinionative and personal woven into the various individual expositions of systems, that, to be impartially fair, each individual must be classed by himself as atheist or theist. Indeed, more upon his own assertion or direct teaching than by reason of any supposed implication in the system he advocates must this classification be made. And if it is correct to consider the subject from this point of view, it is surprising to find to what an exceedingly small number the supposed atheistic ranks dwindle. In company with Socrates, nearly all the reputed Greek atheists strenuously repudiated the charge of teaching that there were no gods. Even Bion, who, according to Diogenes Laertius (Life of Aristippus, XIII, Bohn's tr.), adopted the scandalous moral teaching of the atheist Theodorus, turned again to the gods whom he had insulted, and when he came to die demonstrated in practice what he had denied in theory. As Laertius says in his "Life of Bien", he "who never once said, `I have sinned but spare me'—
Then did this atheist shrink and give his neck
To an old woman to hang charms upon;
And bound his arms with magic amulets;
With laurel branches blocked his doors and windows,
Ready to do and venture anything
Rather than die."
Epicurus, the founder of that school of physics which limited all causes to purely natural ones and consequently implied, if he did not actually assert, atheism, is spoken of as a man whose "piety towards the gods and (whose) affection for his country was quite unspeakable" (ib., Life of Epicurus, V). And though Lucretius Carus speaks of the downfall of popular religion which he wished to bring about (De Rerum Natura, I, 79-80), yet, in his own letter to Henaeceus (Laert., Life of Epicurus, XXVIIA), he states plainly a true theistic position: "For there are gods: for our knowledge of them is indistinct. But they are not of the character which people in general attribute to them." Indeed, this one citation perfectly illustrates the fundamental historic meaning of the term, atheism.
The naturalistic pantheism of the Italian Giordano Bruno (1548-1600) comes near to, if it is not actually a profession of, atheism; while Tomaso Campanella (1568-1639), on the contrary, in his nature-philosophy finds in atheism the one impossibility of thought. Spinoza (1632-77), while defending the doctrine that God certainly exists, so identifies Him with finite existence that it is difficult to see how he can be defended against the charge of atheism even of the first type. In the eighteenth century, and especially in France, the doctrines of materialism were spread broadcast by the Encyclopedists. La Mettrie, Holbach, Feuerbach, Fleurens are usually classed among the foremost materialistic atheists of the period. Voltaire, on the contrary, while undoubtedly helping on the cause of practical atheism, distinctly held its theoretic contrary. He, as well as Rousseau, was a deist. Comte, it will be remembered, refused to be called an atheist. In the last century Thomas Huxley, Charles Darwin, and Herbert Spencer, with others of the evolutionistic school of philosophy, were, quite erroneously, charged with positive atheism. It is a charge which can in no way be substantiated; and the invention and rapid coming into general use of the term agnosticism, used first by Huxley in 1859, shows the long-felt want of a word more definitely defined than atheism to designate a phase of thought either critically or sceptically concerned with the process by which the common tenet of theism is maintained. The fundamental formula is not a denial of the existence of God, but an assertion that The Absolute is unknowable. In Germany, the materialism of Karl Vogt, Jacob Moleschott, Ludwig Buchner, culminating in the monism of Ernst Hackel, goes far towards forming an atheistic system of philosophy. But even the last named admits that there may be a God, though so limited and so foreign to the deity of theists that his admission can hardly remove the system from the first category of theoretic atheism.
Among the unscientific and unphilosophical there have from time to time been found dogmatic atheists of the first type. Here again, however, many of those popularly styled atheists are more correctly described by some other title. There is a somewhat rare tract, "Atheism Refuted in a Discourse to prove the Existence of God by T. P."—British Museum Catalogue, "Tom Paine", who was at one time popularly called an atheist. And perhaps, of the few who have upheld an indubitable form of positive theoretic atheism none has been taken seriously enough to have exerted any influence upon the trend of philosophic or scientific thought. Robert Ingersoll might be instanced, but though popular speakers and writers of this type may create a certain amount of unlearned disturbance, they are not treated seriously by thinking men, and it is extremely doubtful whether they deserve a place in any historical or philosophical exposition of atheism.