| But that my ignorance is absolutely necessary and unavoidable, and that it consequently absolves from the duty of all further investigation, is a fact which cannot be made out upon empirical grounds--from observation--but upon critical grounds alone, that is, by a thoroughgoing investigation into the primary sources of cognition. |
| It follows that the determination of the bounds of reason can be made only on a priori grounds; while the empirical limitation of reason, which is merely an indeterminate cognition of an ignorance that can never be completely removed, can take place only a posteriorI. In other words, our empirical knowledge is limited by that which yet remains for us to know. |
| The former cognition of our ignorance, which is possible only on a rational basis, is a science; the latter is merely a perception, and we cannot say how far the inferences drawn from it may extend. |
| If I regard the earth, as it really appears to my senses, as a flat surface, I am ignorant how far this surface extends. |
| But experience teaches me that, how far soever I go, I always see before me a space in which I can proceed farther; and thus I know the limits--merely visual--of my actual knowledge of the earth, although I am ignorant of the limits of the earth itself. |
| But if I have got so far as to know that the earth is a sphere, and that its surface is spherical, I can cognize a priori and determine upon principles, from my knowledge of a small part of this surface--say to the extent of a degree--the diameter and circumference of the earth; and although I am ignorant of the objects which this surface contains, I have a perfect knowledge of its limits and extent. |
| The sum of all the possible objects of our cognition seems to us to be a level surface, with an apparent horizon--that which forms the limit of its extent, and which has been termed by us the idea of unconditioned totality. |
| To reach this limit by empirical means is impossible, and all attempts to determine it a priori according to a principle, are alike in vain. |
| But all the questions raised by pure reason relate to that which lies beyond this horizon, or, at least, in its boundary line. |
| 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. |