“All ignorance is either ignorance of things or of the functions and limits of knowledge.”
“The determination of the limits of our reason cannot therefore be made save on a priori grounds;”
“on the other hand, that limitation of it which consists merely in an indeterminate knowledge of an ignorance that can never be completely removed, can be recognised a posteriori by reference to that which is possible only through criticism of reason itself, is science.”
“The latter is nothing but perception, and we cannot say how far the inferences from perception may extend.”
“The sum of all the possible objects of our cognition seems to us to be a level surface, with an apparent horizon - that which in its sweep comprehends it all, and which has been entitled by us the idea of unconditioned totality.”
“To reach this concept empirically is impossible, and all attempts to determine it a priori according to a principle, have proved vain.”
“The consciousness of ignorance (unless at the same time this ignorance is recognized as being necessary ought), instead of ending my inquiries, ought rather to be itself the strongest reason for entering upon them.”
“that my ignorance is absolutely necessary, and that I am therefore absolved from all further enquiry, cannot be established empirically, from observation, but only through an examination, critically conducted, of the primary sources of our knowledge”
“David Hume was one of those geographers of human reason who imagine that they have given a sufficient answer to all such questions by declaring them to lie beyond the horizon of human reason - 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 based upon no clear insight, that is, upon no a priori knowledge.”
“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.”
“the criticism of reason, whereby not its present bounds but its determinate and necessary limits, not its ignorance in regard to all possible questions of a certain kind, are demonstrated from principles, and not merely arrived at by way of conjecture.”
“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 cognise; 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.”
“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 facts, 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.”
“he merely declared the understanding to be limited, instead of showing what its limits were; he created a general mistrust in the power of our faculties, without giving us any determinate knowledge of the bounds of our necessary and unavoidable ignorance; he examined and condemned some of the principles of the understanding, without investigating all its powers with the completeness necessary to criticism.”