The theory which places the principle of Certitude in REASON has assumed at least two distinct shapes. In the one it discards all authority except that of private judgment or individual reason; in the other it appeals to a higher reason, which is said to be impersonal and infallible, and which is supposed to regulate and determine the convictions of the human mind. In the former shape, it appears in the speculations of Martineau; in the latter, it is advocated by Cousin; and in one or other of these shapes it constitutes the ground-principle of RATIONALISM. The theory, again, which places the principle of Certitude in AUTHORITY has also assumed two distinct shapes. In the one it speaks of a universal consent or Generic Reason, the reason not of the individual but of the race to which he belongs, and exhibits a singular combination of the Philosophy of Common Sense as taught by Dr. Reid and the Scottish School, with the principle of Authoritative Tradition as taught in the Popish Church; in the other, it refers more specifically, not to the infallibility of the race at large, but to the infallibility of a select body, regularly organized and invested with peculiar powers, into whose hands has been committed the sacred deposit and the sole guardianship of truth, whether in matters of philosophy or faith. In both forms it is presented in the writings of M. Gerbet and M. Lamennais, and in both it is necessary for the full maintenance of the Popish system of doctrine. The theory, again, which places the principle of Certitude in EVIDENCE, admits of being exhibited in two very distinct aspects. In the one, it has been treated as if Evidence were purely _subjective_, as if it belonged exclusively to thought, and not to the object of thought, or as if it depended solely on the perceptions of our minds, and not at all on any objective reality which is independent of them, and which is equally true whether it be perceived by our minds or not. In this form it is a theory of Individualism, and has a strong tendency towards Skepticism. In the other aspect, Evidence is regarded as the sole and sufficient ground of Certitude, but it is viewed both _objectively_ and _subjectively_;--_objectively_, as having its ground and reason in a reality that is independent of our perceptions, and that may or may not be perceived without being the less true or the less certain in itself;--and yet _subjectively_ also, as being equally dependent on certain principles of reason or laws of thought, without which no external manifestation would suffice to create the ideas and beliefs of the human mind, since the evidence which is exhibited externally must not only exist, but must be perceived, discerned, and appreciated, before it can generate belief: but when perceived, it produces conviction, varying in different cases in degree, and amounting in some to absolute certainty, which leaves no room either for denial or doubt.