This book is a slog, but it rewards with a comprehensive system that pushes the bounds of pure reason to its limits. First, Kant has to define terms. “By critique of pure reason… I do not mean a critique of books and systems, but I mean the critique of our power of reason as such, in regard to all cognitions after which reason may strive independently of all experience. Hence I mean by it the decision as to whether a metaphysics as such is possible or impossible…. Transcendental philosophy is the system of all principles of pure reason…. But the critique is not yet that science itself, because it carries the analysis [of a priori concepts] only as far as is required for making a complete judgement about synthetic a priori cognition. The foremost goal in dividing such a science is this: no concepts whatever containing anything empirical must enter into this science.”
Kant next delineates the terms: experiences, intuitions, categories, concepts, and appearances. “All experience, besides containing the senses’ intuition through which something is given, does also contain a concept of an object that is given in intuition, or that appears. Accordingly, concepts of objects as such presumably underlie all experiential cognition as its a priori conditions. Hence presumably the objective validity of all categories, as a priori concepts, rests on the fact that through them alone is experience possible…. Hence the transcendental deduction of all a priori concepts has a principle to which the entire investigation must be directed: viz., the principle that these concepts must be cognized as a priori conditions for the possibility of experience…. If concepts serve as the objective basis for the possibility of experience, then—precisely because of this—they are necessary…. We have a pure imagination, as a basic power of the human soul which underlies a priori all cognition…. By means of this transcendental function of the imagination the two extreme ends, viz., sensibility and understanding, must necessarily cohere; for otherwise sensibility would indeed yield appearances, but would yield no objects of an empirical cognition, and hence no experience. Actual experience consists in apprehension of appearances, their association (reproduction), and thirdly their recognition; in this third [element] (which is the highest of these merely empirical elements of experience), such experience contains concepts, which make possible the formal unity of experience and with it all objective validity (truth) of empirical cognition. Now these bases of the recognition of the manifold, insofar as they concern merely the form of an experience as such, are the categories. Hence the categories underlie all formal unity in the synthesis of imagination…. We cannot think an object except through categories; we cannot cognize an object thought by us except through intuitions corresponding to those concepts. Now all our intuitions are sensible, and this [sensible] cognition is empirical insofar as its object is given. Empirical cognition, however, is experience. Consequently no cognition is possible for us a priori except solely of objects of possible experience…. As far as pure intuitions as well as pure concepts of understanding are concerned, they are elements of cognition that are found in us a priori.”
Next, Kant explicates the difference between analytic and synthetic judgements. “The supreme principle of all synthetic judgments is this: Every object is subject to the conditions necessary for synthetic unity of the manifold of intuition in a possible experience. Thus synthetic judgments are possible a priori if we refer the formal conditions of a priori intuition, the synthesis of imagination, and the necessary unity of this synthesis in a transcendental apperception to a possible experiential cognition as such.” Next, the difference between understanding and experience. “Everything that understanding draws from itself, rather than borrows from experience, it still has for the sake of nothing other than use in experience only. The principles of pure understanding—whether constitutive a priori (like the mathematical principles) or merely regulative (like the dynamical ones)—contain nothing but, as it were, the pure schema for possible experience. For experience has its unity solely from the synthetic unity that the understanding confers, originally and on its own, on the synthesis of imagination by reference to apperception; appearances, as data for a possible cognition, must a priori already have reference to, and be in harmony with, that synthetic unity. Now, these rules of understanding not only are true a priori; but, by containing the basis for the possibility of experience as the sum of all cognition wherein objects may be given to us, they are even the source of all truth.”
Kant moves on to cognition and reason. “All our cognition starts from the senses, proceeds from there to understanding, and ends with reason, beyond which there is found in us nothing higher to work on the material of intuition and bring it under the highest unity of thought…. There is of reason, as there is of understanding, a merely formal—i.e., logical—use, where reason abstracts from all content of cognition. But there is also a real use, where reason itself contains the origin of certain concepts and principles that it borrows neither from the senses nor from understanding…. We shall distinguish reason from understanding by calling it our power of principles…. I would, therefore, call cognition from principles only that cognition wherein I cognize the particular in the universal through concepts. Thus any syllogism is a form of deriving a cognition from a principle…. The understanding may be considered a power of providing unity of appearances by means of rules; reason is then the power of providing unity of the rules of understanding under principles. Hence reason initially never deals with experience or any object, but deals with the understanding in order to provide the understanding’s manifold cognitions with a priori unity through concepts…. The designation, concept of reason, even if considered provisionally, already shows that such a concept refuses to be confined within experience…. Concepts of reason serve for comprehending, whereas concepts of understanding serve for understanding (viz., perceptions). If concepts of reason contain the unconditioned, then they concern something to which all experience is subject but which itself is never an object of experience.”
Kant explains idealism. “The existence of all objects of outer senses is doubtful. I call this uncertainty the ideality of outer appearances, and the doctrine of this ideality is called idealism…. Only what is in ourselves can be perceived directly…. Therefore the existence of an actual object outside me (if this word is taken in its intellectual meaning) is never given straightforwardly in perception. Rather, perception is a modification of inner sense…. Hence, I cannot, in fact, perceive external things, but can only infer their existence from my inner perception…. Hence by an idealist we must mean, not someone who denies the existence of external objects of the senses, but someone who merely does not grant that this existence is cognized through direct perception, and who infers from this that we can never through any possible experience become completely certain of their actuality…. By transcendental idealism of all appearances I mean the doctrinal system whereby we regard them, one and all, as mere presentations and not things in themselves.”
Finally, Kant tentatively begins to pick through his theme, pure reason. “Apart from transcendental philosophy, there are two further pure rational sciences, the one having a merely speculative and the other a practical content: pure mathematics and pure morality.” Kant moves on to pure reason’s relationship with time and, therefore, causality and free will. “Pure reason, as a merely intelligible power, is not subjected to the form of time, nor consequently to the conditions of temporal succession. The causality of reason in its intelligible character by no means arises, or starts at a certain time, in order to produce an effect…. Of reason… one cannot say that the state wherein it determines the power of choice is preceded by another state wherein that state itself is determined…. Hence reason is the permanent condition of all the voluntary actions under which the human being appears. Each of these actions, even before it occurs, is predetermined in the human being’s empirical character. But in regard to the intelligible character, of which the empirical character is only the sensible schema, no before or after holds, and every action—regardless of its time relation to other appearances—is the direct effect of the intelligible character of pure reason…. In reason there is no antecedent state determining the subsequent state, and that reason therefore does not belong at all in the series of sensible conditions that make appearances necessary according to natural laws. Reason is present to, and is the same in, all actions of the human being in all circumstances of time…. Pure reason is in fact occupied with nothing but itself. Nor can it have any other business. For what are given to it are not objects for the unity of the experiential concept, but cognitions of understanding for the unity of the concept of reason, i.e., for the unity of coherence in a principle. The unity of reason is the unity of a system.”
Kant now circles back around to the reality of the transcendental and to the nature of God. “One asks, first, whether there is something that is distinct from the world and contains the basis of the world order and of the coherence thereof according to universal laws, then the answer is: without doubt. For the world is a sum of appearances; hence there must be some basis of these appearances that is transcendental, i.e., thinkable only for the pure understanding. If the question is, second, whether this being is substance, and of the greatest reality, and necessary, etc., then I answer that this question has no signification whatever. For all the categories through which I try to frame a concept of such an object have only an empirical use, and have no meaning whatever unless they are applied to objects of possible experience, i.e., to the world of sense.”
Kant explains the differences between philosophy and math. “Philosophical cognition is rational cognition from concepts. Mathematical cognition is rational cognition from the construction of concepts. But to construct a concept means to exhibit a priori the intuition corresponding to it. Hence construction of a concept requires a nonempirical intuition. Consequently this intuition, as intuition, is an individual object; but as the construction of a concept (a universal presentation), it must nonetheless express in the presentation its universal validity for all possible intuitions falling under the same concept…. Hence philosophical cognition contemplates the particular only in the universal. Mathematical cognition, on the other hand, contemplates the universal in the particular, and indeed even in the individual…. Hence the essential difference between these two kinds of rational cognition consists in this difference of form, and does not rest on the difference of their matter or [i.e.] objects…. Philosophy keeps to universal concepts only. Mathematics can accomplish nothing with the mere concept but hastens at once to intuition, in which it contemplates the concept in concreto, but yet not empirically; rather mathematics contemplates the concept only in an intuition that it exhibits a priori.” Kant also breaks down the difference in proofs of affirmation versus those of negation. “For no matter how modest and moderate someone may look who behaves toward the assertions of others in a merely declining and negating manner, yet as soon as he wants to make his objections hold as proofs of the opposite assertion, his claim is always just as haughty and imaginary as if he had adopted the affirming party and its assertion.”
Kant circles back to the relationship between appearances and pure reason. “In appearance, through which all objects are given to us, there are two components: the form of intuition (space and time), which can be cognized and determined completely a priori; and the matter (the physical [component] or content [of intuition], which signifies a something encountered in space and time and hence a something containing existence and corresponding to sensation…. You can say that properly speaking all life is intelligible only and not subjected to changes of time, and that it neither began through birth nor is ended through death; but that this life, on the other hand, is nothing but a mere appearance, i.e. a sensible presentation of the pure spiritual life, and the whole world of sense is a mere image hovering before our current way of cognizing, and like a dream has in itself no objective reality…. This is the fate of all assertions of pure reason: They [are synthetic propositions that] go beyond the conditions of all possible experience—the conditions outside of which no documentation of truth is anywhere to be found. But such assertions must nonetheless employ the laws of understanding; and these laws are determined merely for empirical use, yet without them no step can be taken in any synthetic thought.”
Kant, again, explicitly takes up the transcendental challenges of belief in God, free will, and the soul. “When I hear that an uncommon mind is supposed to have demonstrated away the freedom of the human will, the hope for a future life, and the existence of God, then I am eager to read his book; for in view of his talent I expect him to further my insights. That in fact he will have accomplished nothing of all this—this I already know beforehand with complete certainty…. Metaphysics has only three ideas as the proper purpose of its investigation—God, freedom, and immortality.... Everything else that this science deals with serves it only as a means for arriving at these ideas and at their reality.... Insight into these ideas would make theology, morality, and—through combination of the two—religion and hence the highest purposes of our existence dependent merely on our speculative power of reason and on nothing else.”
Kant concludes with a discussion on morality. “The moral law at least can rest on mere ideas of pure reason and thus be cognized a priori. I assume that there actually are pure moral laws that determine completely a priori (without regard to empirical motives, i.e., to happiness) the doing and the refraining, i.e., the use of the freedom of a rational being as such, and that these laws command absolutely (not merely hypothetically, on the presupposition of other empirical purposes) and are therefore necessary in every regard…. Hence pure reason contains—although not in its speculative use but still in a certain practical, viz., the moral, use—principles of the possibility of experience, viz., of the experience of such actions as could be encountered in accordance with moral precepts…. And hence a particular kind of systematic unity must be possible, viz., moral unity…. Accordingly, the principles of pure reason in its practical use—but specifically in its moral use—have objective reality…. The moral world is a mere idea; yet it is a practical idea that actually can and ought to have its influence on the world of sense…. The system of morality is linked inseparably—but only in the idea of pure reason—with the system of happiness…. The idea of such an intelligence wherein the morally most perfect will, combined with the highest bliss, is the cause of all happiness in the world, insofar as this happiness is exactly proportionate to one’s morality (as the worthiness to be happy), I call the ideal of the highest good…. Hence happiness, in exact balance with the morality of rational beings whereby these beings are worthy of happiness, alone amounts to the highest good of a world into which, according to the precepts of pure but practical reason, we must definitely transfer ourselves. That world, to be sure, is only an intelligible one; for the world of sense does not promise to us, as arising from the nature of things, such systematic unity of purposes. Moreover, the reality of that intelligible world cannot be based on anything other than the presupposition of a highest original good: a good where independent of reason, equipped with all the sufficiency of a supreme cause, establishes, preserves, and completes—according to the most perfect purposiveness—the order of things that is universal although very much concealed from us in the world of sense.”
