It may be useful to preface our criticism by a classification of the various theistic theories, rather as a provisional chart of opinion, than as an exhaustive summary of all the arguments which have been advanced, or of all possible varieties in the mode of proof. Many thinkers, perhaps the majority, and notably the mediæval schoolmen, have combined several distinct lines of evidence; and have occasionally borrowed from a doctrine which they explicitly reject some of the very elements of their argument. They have often forsaken their own theory at a crisis, and not observed their departure from the data on which they profess exclusively to build.

The first class of theories are strictly ontological or ontotheological. They attempt to prove the objective existence of Deity from the subjective notion of necessary existence in the human mind, or from the assumed objectivity of space and time which they interpret as the attributes of a necessary substance.

The second are the cosmological or cosmo-theological proofs. They essay to prove the existence of a supreme self-existent cause from the mere fact of the existence of the world, by the application of the principle of causality. Starting with the postulate of any single existence whatsoever, the world or anything in the world, and proceeding to argue backwards or upwards, the existence of one supreme cause is held to be 'a regressive inference' from the existence of these effects. As there cannot be, it is alleged, an infinite series of derived or dependent effects, we at length reach the infinite or uncaused cause. This has been termed the proof from contingency, as it rises from the contingent to the necessary, from the relative to the absolute. But the cosmological proof may have a threefold character, according as it is argued: 1. That the necessary is the antithesis of the contingent; or, 2. That because some being now exists, some being must have always existed; or, 3. That because we now exist and have not caused ourselves, some cause adequate to produce us, must also now exist.

A third class of proofs are somewhat inaccurately termed physico-theological, a phrase equally descriptive of them and of those last mentioned. They are rather teleological or teleotheological. The former proof started from any finite existence. It did not scrutinise its character, but rose from it to an absolute cause, by a direct mental leap or inference. This scrutinises the effect, and finds traces of intelligence within it. It detects the presence or the vestiges of mind in the particular effect it examines, viz., the phenomena of the world, and from them it infers the existence of Deity. One branch of it is the popular argument from design, or adaptation in nature, the fitness of means to ends implying, it is said, an architect or designer. It may be called techno-theology, and is variously treated according as the technologist (α) starts from human contrivance and reasons to nature, or (β) starts from nature's products and reasons toward man. Another branch is the argument from the order of the universe, from the types or laws of nature, indicating, it is said, an orderer or law-giver, whose intelligence we thus discern. It is not, in this case, that the adjustment of means to ends proves the presence of a mind that has adjusted these. But the law itself, in its regularity and continuity, implies a mind behind it, an intelligence animating the otherwise soulless universe. It might be termed nomo-theology or typo-theology. Under the same general category may be placed the argument from animal instinct, which is distinct at once from the evidence of design and that of law or typical order. To take one instance: The bee forms its cells, following unconsciously, and by what we term 'instinct,' the most intricate, mathematical, laws. There is mind, there is thought in the process; but whose mind, whose thought? Not the animal's, because it is not guided by experience. The result arrived at is a result which could be attained by man only through the exercise of reason of the very highest order. And the question arises, are we not warranted in supposing that a hidden pilot guides the bee, concealed behind what we call its instinct. We do not, meanwhile, discuss the merit of this argument; but merely indicate the difference between it and the argument from design, and that from law and order. It is not a question of the adjustment of phenomena. It is the demand of the intellect for a cause adequate to account for a unique phenomenon. It approaches the cosmo-theological argument as closely as it approaches the techno-theological one; yet it is different from both. The cosmo-theological rises from any particular effect, and by a backward mental bound reaches an infinite first cause. The techno-theological attempts to rise from the adjustment of means to ends, to an adjuster or contriver. This simply asks, whence comes the mind that is here in operation, perceived by its effects?

The next class of arguments are based upon the moral nature of man. They may be termed in general ethico-theological; and there are, at least, two main branches in this line of proof. The former is the argument from conscience as a moral law, pointing to Another above it; the law that is 'in us, yet not of us'—not the 'autonomy' of Kant, but a theonomy—bearing witness to a legislator above. It is the moral echo within the soul of a Voice louder and vaster without. And, as evidence, it is direct and intuitive, not inferential. The latter is the argument of Kant, (in which he was anticipated by several, notably by Raimund of Sabunde.) It is indirect and inferential, based upon the present phenomena of our moral nature. The moral law declares that evil is punishable and to be punished, that virtue is rewardable and to be rewarded; but in this life they are not so: therefore, said Kant, there must be a futurity in which the rectification will take place, and a moral arbiter by whom it will be effected.

Finally, there is the argument, which, when philosophically unfolded, is the only unassailable stronghold of theism, its impregnable fortress, that of intuition. As it is simply the utterance or attestation of the soul in the presence of the Object which it does not so much discover by searching, as apprehend in the art of revealing itself, it may be called (keeping to the analogy of our former terms) eso-theological or esoterico-theological. It is not an argument, an inference, a conclusion. It is an attestation, the glimpse of a reality which is apprehended by the instinct of the worshipper, and through the poet's vision, as much as by the gaze of the speculative reason. It is not the verdict of one part of human nature, of reason, or the conscience, the feelings, or the affections; but of the whole being, when thrown into the poise or attitude of recognition, before the presence of the self-revealing object. There are several phases of this, which we term the eso-theological proof. We see its most rudimental traces in the polytheism of the savage mind, and its unconscious personification of nature's forces. When this crude conception of diverse powers in partial antagonism gives place to the notion of one central power, the instinct asserts itself in the common verdict of the common mind as to One above, yet kindred to it. It is attested by the feeling of dependence, and by the instinct of worship, which witnesses to some outward object corresponding to the inward impulse, in analogy with all the other instincts of our nature. It is farther attested by the poet's interpretation of nature, the verdict of the great seers, that the universe is pervaded by a supreme Spirit, 'haunted for ever by the eternal mind.' We find its highest attestation in that consciousness of the Infinite itself which is man's highest prerogative as a rational creature. We have thus the following chart of theistic theories.

In addition, we might mention several subsidiary or sporadic proofs which have little or no philosophical relevancy, but which have some theological suggestiveness, viz., 1. The historical consensus. 2. The felicity of the theist. 3. The testimony of revelation.

It is unnecessary to discuss all these alleged proofs at length; but the powerlessness of the most of them to establish the transcendent fact they profess to reach, demands much more serious thought than it has yet received.

The ontological proof has always possessed a singular fascination for the speculative mind. It promises, and would accomplish so much, if only it were valid. It would be so powerful, if only it were conclusive. But had demonstration been possible, the theistic argument, like the proofs of mathematics, would have carried conviction to the majority of thinkers long ago. The historical failure is signal. Whether in the form in which it was originally cast by Augustine, Anselm, and Aquinas, or in the more elaborate theory of Descartes, or as presented by the ponderous English minds of Cudworth, Henry More, and Dr. Samuel Clarke, it is altogether a petitio principii. Under all its modifications, it reasons from the necessary notion of God, to his necessary existence; or from the necessary existence of space and time, which are assumed to be the properties or attributes of a substance, to the necessary existence of that substance. A purely subjective necessity of the reason is carried from within, and held conclusive in the realm of objective reality. But the very essence of the problem is the discovery of a valid pathway by which to pass from the notions of the intellect to the realities of the universe beyond it; we may not, therefore, summarily identify the two, and at the outset take the existence of the one as demonstrative of the other. In the affirmation of real existence we pass from the notion that has entered the mind (or is innate), to the realm of objective being, which exists independently of us who affirm it; and how to pass warrantably from the ideal world within to the real world without is the very problem to be solved. To be valid at its starting-point, the ontological argument ought to prove that the notion of God is so fixed in the very root of our intelligent nature that it cannot be dislodged from the mind; and this some thinkers, such as Clark, have had the hardihood to affirm. To be valid as it proceeds, it ought to prove that the notion thus necessary in thought, has a real counterpart in the realm of things, in order to vindicate the step it so quietly takes from the ideal notion to the world of real existence. It passes from thought to things, as it passes from logical premiss to conclusion. But to be logical, it must rest contented with an ideal conclusion deduced from its ideal premises. And thus, the only valid issue of the ontological argument is a system of absolute idealism, of which the theological corollary is pantheism. But as this is not the Deity the argument essays to reach, it must be pronounced illogical throughout.