Immanuel Kant (1724-1804) Critique of Pure Reason .

Background & Preface to the Second Edition

"Our knowledge is conversant about our ideas only. Since the mind, in all its thoughts and reasonings, hath no other immediate object but its own ideas, which it alone does or can contemplate, it is evident that our knowledge is only conversant about them. " (Locke IV: I:1).

"Hume, by his consistency, showed that empiricism carried to its logical conclusion, led to results that few human beings could bring themselves to accept, and abolished, over the whole field of science. the distinction between rational belief and credulity. 
Locke had foreseen this danger. He puts into the mouth of a supposed critic the argument: "If knowledge consists in agreement of ideas, the enthusiast [fanatic] and the sober man are on a level." (Russell, p.703) {2}

1.      Knowledge, as has been shown, consists in the perception of the agreement or disagreement of ideas. (Locke, IV:vii:1) 

2.      If it be true, that all knowledge lies only in the perception of the agreement or disagreement of our own ideas, the visions of an enthusiast [fanatic] and the reasonings of a sober man will be equally certain. It is no matter how things are: so a man observes but the agreement of his own imaginations, and talk conformably, it is all truth, all certainty. Such castles in the air will be as strongholds of truth, as the demonstrations of Euclid. That an harpy is not a centaur is by this way as certain knowledge, and as much a truth, as that a square is not a circle. (Locke IV: iv:1) 

3.      The . . . simple ideas . . . must necessarily be the product of things operating on the mind, in a natural way, and producing therein those perceptions which by the Wisdom and Will of our Maker they are ordained and adapted to. (Locke IV:iv:4) 

4.      Whether the treatment of such knowledge as lies within the province of reason does or does not follow the secure path of a science, is easily to be determined from the outcome. For if after elaborate preparations, frequently renewed, it is brought to a stop immediately it nears its goal; if often it is compelled to retrace its steps and strike into some new line of approach; or again, if the various participants are unable to agree in any common plan of procedure, then we may rest assured that is very far from having entered upon the secure path of a science, and is merely random groping. In these circumstances, we shall be rendering a service to reason should we succeed in discovering the path upon which it can securely travel, even if, as a result of so doing, much that is comprised in our original aims, adopted without reflection, may have to be abandoned as fruitless. (Bviii) 

5.      So far, too, are the students of metaphysics from exhibiting any kind of unanimity in their contentions, that metaphysics has rather to be regarded as a battle-ground quite peculiarly suited for those who desire to exercise themselves in mock combats, and in which no participant has ever yet succeeded in gaining even so much as an inch of territory, not at least in such manner as to secure him in its permanent possession. This shows, beyond all questioning, that the procedure of metaphysics has hitherto been a merely random groping, and, what is worst of all, a groping among mere concepts. (Bxv) 

6.      On a cursory view of the present work it may seem that its results are merely negative, warning us that we must never venture with speculative reason beyond the limits of experience. Such is in fact its primary use.  

7.      [T]he new point of view enables us to explain how there can be knowledge a priori; and, in addition, to furnish satisfactory proofs of the laws which form the a priori basis of nature, regarded as the sum of the objects of experience -- neither achievement being possible on the procedure hitherto followed. (Bxxiv) 

Overview of the Critique

If you always wore blue spectacles, you could be sure of seeing everything blue (this is not Kant's illustration). Similarly, since you always wear spatial spectacles in your mind, you are sure of always seeing everything in space. (Russell, p.707-8) 

As regards cause however, there is an inconsistency, for the things in themselves are regarded by Kant as the causes of sensations, and free volitions are held by him to be causes of occurrences in space and time. This inconsistency is not an accidental oversight, it is an essential part of his system. (Russell, p. 708) {7}

12.  'Being' is obviously not a real predicate; that is, it is not a concept of something which could be added to the concept of a thing. It is merely the positing of a thing, or of certain determinations, as existing in themselves. Logically, it is merely the copula of a judgment. The proposition, 'God is omnipotent', contains two concepts, each of which has its object -- God and omnipotence. The small word 'is' adds no new predicate, but only serves to posit the predicate in relation to the subject. (626-627) 

13.  Experience teaches us that a thing is so and so, but not that it cannot be otherwise. (B3)  

1.      If he is to know anything with a priori certainty [the geometer] must not ascribe to the figure anything save what necessarily follows from what he has himself set into it in accordance with his concept. (Bxii) 

2.      [Reason] must approach nature in order to be taught by it. It must not, however, do so in the character of a pupil who listens to everything that the teacher chooses to say, but of an appointed judge who compels the witnesses to answer questions which he has himself formulated. (Bxiii) 

3.      Hitherto it has been assumed that all our knowledge must conform to objects. . . . We must therefore make trial whether we may not have more success in the tasks of metaphysics, if we suppose that objects must conform to our knowledge. This would agree better with what is desired, namely, that it should be possible to have knowledge of object a priori, determining something in regard to them prior to their being given. (Bxvi 

4.      If intuition must conform to the constitution of objects, I do not see how we could know anything of the latter a priori; but if the object (as object of the senses) must conform to the constitution of our faculty of intuition, I have no difficulty in conceiving such a possibility. (Bxvii) 

5.      [A priori] knowledge has only to do with the appearances, and must leave the thing in itself as indeed real per se, but as not known by us. For what necessarily forces us to transcend the limits of experience and of all appearances is the unconditioned, which reason, by necessity and by right, demands in things in themselves, as required to complete the series of conditions. (Bxx) 

6.      [N]othing in a priori knowledge can be ascribed to objects save what the thinking subject derives from itself . . . (Bxxiii

7.      At least this is so, immediately we are convinced that there is an absolutely necessary practical employment of pure reason -- the moral -- in which in inevitably goes beyond the limits of sensibility. (Bxxv) 

8.      [T]here is no contradiction [given that "object" has both phenomenal and a noumenal senses] in supposing that one and the same will is, in the appearance, that is, in its visible acts necessarily subject to the law of nature, and so far not free, while yet, as belonging to a thing in itself, is not subject to that law and is therefore free. My soul, viewed from the latter standpoint, cannot indeed be known by means of speculative reason (and still less through empirical observation); and freedom as a property of a being to which I attribute effects in the sensible world, is therefore also not knowable in such a fashion. (Bxxviii) 

9.      Thus it does indeed follow that all possible speculative knowledge of reason is limited to mere objects of experience. But our further contention must also be duly borne in mind, namely, that though We cannot know these objects as things in themselves, we must yet be in position at least to think them as things in themselves;} otherwise we should be landed in the absurd conclusion that there can be appearance without anything that appears. (Bxxvii) 

10.  [M]orality necessarily presupposes freedom (in the strictest sense) as a property of our will . . . [since] it yields practical principles -- original principles, proper to our reason -- as a priori data of reason, and . . . this would be absolutely impossible save on the assumption of freedom . . . (Bxxviii)

11.     I have therefore found it necessary to deny knowledge, in order to make room for faith. (Bxxx


15.      Now the proper problem of pure reason is contained in the question: How are a priori synthetic judgments possible? (B19) 

16.      Thus the critique of reason, in the end, necessarily leads to scientific knowledge; while its dogmatic employment, on the other hand, lands us in dogmatic assertions to which other assertions, equally specious, can always be opposed -- that is, in skepticism. (B22-23) 

17.      I entitle transcendental all knowledge which is occupied not so much with objects as with the mode of our knowledge of objects in so far as this mode of knowledge is to be possible a priori. (B25) 

18.     [T]here are two stems of human knowledge, namely, sensibility and understanding, which perhaps spring from a common, but to us unknown, root. Through the former, objects are given to us; through the latter, they are thought. (B29)

19.  "Thoughts without content are empty, intuitions without concepts are blind." (B75)

1.        But though all our knowledge begins with experience, it does not follow that it all arises out of experience. For it may well be that even our empirical knowledge is made up of what we receive through impressions and of what our own faculty of knowledge (sensible impressions serving merely as the occasion) supplies from itself. (B1) 

2.        [W]e shall understand by a priori knowledge, not knowledge independent of this or that experience, but knowledge absolutely independent of all experience. Opposed to it is empirical knowledge, which is knowledge possible only a posteriori, that is, through experience. (B2-3) 

3.        [E]xperience never confers on its judgments true or strict but only assumed and comparative universality, through induction. (B3) 

4.        Necessity and strict universality are, thus, sure criteria of a priori knowledge. (B4) 

5.        [T]he very concept of a cause so manifestly contains the concept of a necessity of connection with an effect and of the strict universality of the rule, that the concept would be altogether lost if we attempted to derive it, as Hume has done, from a repeated association of that which happens with that which precedes, and from a custom of connecting representations, a custom originating in this repeated association, and constituting therefore a merely subjective necessity. (B5) 

6.        Such a priori origin is manifest in certain concepts, no less than in judgments. (B5) 

7.        Owing, therefore, to the necessity with which this concept of substance forces itself upon us, we have no option save to admit that it has its seat in our faculty of a priori knowledge. (B6) 

8.        But what is still more extraordinary than all the preceding is this, that certain modes of knowledge leave the field of all possible experiences and have the appearance of extending the scope of our judgments beyond all limits of experience, and this by means of concepts to which no corresponding object can ever be given in experience. (B7) 

9.        These unavoidable problems set by pure reason itself are God, freedom, and immortality. (B7) 

10.     In all judgments in which the relation of a subject to the predicate is thought (I take into consideration affirmative judgments only, the subsequent application to negative judgments being easily made), this relation is possible in two different ways. Either the predicate to the subject A, as something which is (covertly) contained in this concept A; or outside the concept A, although it does indeed stand in connection with it. In the one case I entitle the judgment analytic, in the other synthetic. (B10) 

11.     Analytic judgments (affirmative) are therefore those in which the connection of the predicate with the subject is thought through identity; those in which this connection is thought without identity should be entitled synthetic. The former, as adding nothing through the predicate to the concept of the subject, but merely breaking it up into those constituent concepts that have all along been thought in it, although confusedly, can also be entitled explicative. The latter, on the other hand, add to the concept of the subject a predicate which has not been in any wise thought in it, and which no analysis could possibly extract from it; and they may therefore be entitled ampliative. (B10-11) 

12.     Judgments of experience, as such, are one and all synthetic. (B11) 

13.     All mathematical judgments, without exception, are synthetic. (B14) 

14.   Metaphysics . . . ought to contain a priori synthetic knowledge. For its business is not merely to analyze concepts which we make for ourselves a priori of things, and thereby to clarify them analytically, but to extend our a priori knowledge. (B18) 

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