The celebrated David Hume was one of those geographers of human reason who believe that they have given a sufficient answer to all such questions by declaring them to lie beyond the horizon of our knowledge- a horizon which, however, Hume was unable to determine.His attention especially was directed to the principle of causality; and he remarked with perfect justice that the truth of this principle, and even the objective validity of the conception of a cause, was not commonly based upon clear insight, that is, upon a priori cognition.
Hence he concluded that this law does not derive its authority from its universality and necessity, but merely from its general applicability in the course of experience, and a kind of subjective necessity thence arising, which he termed habit.From the inability of reason to establish this principle as a necessary law for the acquisition of all experience, he inferred the nullity of all the attempts of reason to pass the region of the empirical.
This procedure of subjecting the facta of reason to examination, and, if necessary, to disapproval, may be termed the censura of reason.This censura must inevitably lead us to doubts regarding all transcendent employment of principles.But this is only the second step in our inquiry.The first step in regard to the subjects of pure reason, and which marks the infancy of that faculty, is that of dogmatism.The second, which we have just mentioned, is that of scepticism, and it gives evidence that our judgement has been improved by experience.But a third step is necessary- indicative of the maturity and manhood of the judgement, which now lays a firm foundation upon universal and necessary principles.This is the period of criticism, in which we do not examine the facta of reason, but reason itself, in the whole extent of its powers, and in regard to its capability of a priori cognition; and thus we determine not merely the empirical and ever-shifting bounds of our knowledge, but its necessary and eternal limits.We demonstrate from indubitable principles, not merely our ignorance in respect to this or that subject, but in regard to all possible questions of a certain class.Thus scepticism is a resting place for reason, in which it may reflect on its dogmatical wanderings and gain some knowledge of the region in which it happens to be, that it may pursue its way with greater certainty; but it cannot be its permanent dwelling-place.It must take up its abode only in the region of complete certitude, whether this relates to the cognition of objects themselves, or to the limits which bound all our cognition.
Reason is not to be considered as an indefinitely extended plane, of the bounds of which we have only a general knowledge; it ought rather to be compared to a sphere, the radius of which may be found from the curvature of its surface- that is, the nature of a priori synthetical propositions- and, consequently, its circumference and extent.Beyond the sphere of experience there are no objects which it can cognize; nay, even questions regarding such supposititious objects relate only to the subjective principles of a complete determination of the relations which exist between the understanding-conceptions which lie within this sphere.
We are actually in possession of a priori synthetical cognitions, as is proved by the existence of the principles of the understanding, which anticipate experience.If any one cannot comprehend the possibility of these principles, he may have some reason to doubt whether they are really a priori; but he cannot on this account declare them to be impossible, and affirm the nullity of the steps which reason may have taken under their guidance.He can only say:
If we perceived their origin and their authenticity, we should be able to determine the extent and limits of reason; but, till we can do this, all propositions regarding the latter are mere random assertions.In this view, the doubt respecting all dogmatical philosophy, which proceeds without the guidance of criticism, is well grounded; but we cannot therefore deny to reason the ability to construct a sound philosophy, when the way has been prepared by a thorough critical investigation.All the conceptions produced, and all the questions raised, by pure reason, do not lie in the sphere of experience, but in that of reason itself, and hence they must be solved, and shown to be either valid or inadmissible, by that faculty.
We have no right to decline the solution of such problems, on the ground that the solution can be discovered only from the nature of things, and under pretence of the limitation of human faculties, for reason is the sole creator of all these ideas, and is therefore bound either to establish their validity or to expose their illusory nature.
The polemic of scepticism is properly directed against the dogmatist, who erects a system of philosophy without having examined the fundamental objective principles on which it is based, for the purpose of evidencing the futility of his designs, and thus bringing him to a knowledge of his own powers.But, in itself, scepticism does not give us any certain information in regard to the bounds of our knowledge.All unsuccessful dogmatical attempts of reason are facia, which it is always useful to submit to the censure of the sceptic.But this cannot help us to any decision regarding the expectations which reason cherishes of better success in future endeavours; the investigations of scepticism cannot, therefore, settle the dispute regarding the rights and powers of human reason.
