Atheism invariably presupposes and perpetuates practical ungodliness; and that the latter has also a tendency to produce the former, since the habitual disregard of God in the practical conduct of life indicates a state of mind in which men are peculiarly exposed to the seductions of infidelity and prone to yield to them, especially in seasons of revolutionary excitement or of prevailing epidemic unbelief. It would be wrong to rank every ungodly man among professed or even conscious Atheists, for he may never have denied or even doubted the existence and government of God; yet it were equally wrong to represent or treat him as a true believer, since he shows that, practically, "God is not in all his thoughts;" and hence the necessity of our first distinction between theoretical or speculative, and practical or habitual Atheism.

Speculative Atheism, again, is either dogmatic or skeptical. It is dogmatic, when it amounts to an affirmation, either that there is no God, or that the question of his existence is necessarily insoluble by the human faculties. Atheism has been distinguished from Anti-theism; and the former has been supposed to imply merely the non-recognition of God, while the latter asserts His non-existence. This distinction is founded on the difference between unbelief and disbelief;[15] and its validity is admitted in so far as it discriminates merely between dogmatic and skeptical Atheism. But Anti-theism is maintained, in the strictest sense of the term, where it is affirmed either that there is no God, or that the existence of the Supreme Being cannot in any circumstances become an object of human knowledge. In each of these forms, Atheism is dogmatic; it denies the existence of God, or it denies the possibility of His being known. But there is also a skeptical Atheism, which does not affirm absolutely either that there is no God, or that the knowledge of God is necessarily excluded by the limitations of human reason, but contents itself with saying, "non-liquet,"—i.e., with denying the sufficiency of the evidence. It answers every appeal to that evidence by saying that, however satisfactory it may be to the minds of some, it does not carry conviction to the minds of all, and that for this reason it may be justly regarded as doubtful or inconclusive. These two forms of Atheism—the Dogmatic and the Skeptical—are widely different from each other; they rest on distinct grounds, and they require, therefore, to be discussed separately, each on its own peculiar and independent merits. The Dogmatic Atheist feels no force in the arguments which are directed merely against his skeptical ally; for, strong in his own position and confident in his ability to maintain it, he is conscious of no speculative doubt, and affirms boldly what he unhesitatingly believes. The Skeptical Atheist, again, feels no force in the arguments which are directed against a Dogmatic System such as he utterly disclaims; he is equally unwilling to affirm either that there is, or that there is not, a God: he takes refuge in doubt, and refuses alike to affirm or to deny; his only plea is, the want or the weakness of evidence on either side. From this radical difference between the two forms of Speculative Atheism, there arises a necessity for discussing each of them on its own merits; and yet, although theoretically they may be easily distinguished, it will be found that practically they are often conjoined, since the same mind will often fluctuate between the two, and shift its ground by betaking itself alternately to the one or the other, according to the exigencies of the argument. Assail the Dogmatic Atheist with the unanswerable statement of John Foster, that it would require nothing less than Omniscience to warrant the denial of a God, and he will probably defer to it so far as to admit that he cannot prove his negative conclusion, but will add that he is not bound to do so, and that all that can be reasonably required of him is to show that the evidence adduced on the opposite side is insufficient to establish the Divine existence, or that the phenomena which supply that evidence may be as well, or more satisfactorily, explained in some other way. Assail, in like manner, the Skeptical Atheist with the self-evident truth that, even on his own principles, he is not entitled to assume or to act upon the assumption, that there is no God, since the result of his reasonings is doubt merely, and such doubt as implies that there may be a Creator, Governor, and Judge, he will probably defer to it so far as to admit that this is the only logical result of his system, but will add that, where there is no conclusive evidence on either side, there can be no moral obligation to a religious life, and no guilt in living "without God in the world." It will be found, too, that, distinct as these two forms of Speculative Atheism may appear to be, yet they have often been made to rest on a common ground, and the self-same arguments have been adduced in support of both. Thus the doctrine of Materialism, the theory of Development, and the system of Natural Laws, have all been applied by the Dogmatic Atheist to justify his denial of the existence and government of God, on the ground that all the phenomena of Nature may be accounted for without the supposition of a Supreme Mind; while the very same doctrines or theories have been also applied by the Skeptical Atheist to justify, not his denial, but his doubt, and to vindicate his verdict of "non-liquet" on the evidence adduced. And as the same arguments are often employed by both parties in support of their respective views, so they make use, for the most part, of the same objections in assailing the cause of Theism; insomuch that it would be impossible, and even were it possible it would be superfluous, to attempt a formal refutation of either, without discussing those more general principles which are applicable to both. For this reason, we propose to examine in the sequel the various theories which have been applied in support alike of Dogmatic and of Skeptical Atheism, so as to illustrate the grounds that are common to both, while we consider also the distinctive peculiarities of the two systems, and more particularly the grounds of Religious Skepticism.

Besides the radical distinction between Dogmatic and Skeptical Atheism, we must consider the difference between the four great leading systems which have been applied to account for the existing order of Nature, without the recognition of a living, intelligent, personal God. There are many specific varieties of Atheism; but, ultimately, they may be reduced to four classes. The first system assumes and asserts the eternal existence of the Cosmos; that is, of the present order of Nature, with all its laws and processes, its tribes and races, whether of vegetable or animal life; and affirms that the world, as now constituted, never had a beginning, and that it will never have an end. This has been called the Aristotelian Hypothesis, because Aristotle, while he spoke of a Supreme Mind or Reason, maintained not only the eternity of matter, but also the eternity of "substantial forms and qualities."

The second system affirms, not the eternal existence of the Cosmos,—for the commencement of the existing order of Nature is admitted to be comparatively recent,—but the eternal existence of Matter and Motion; and