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Title page of the 1781 edition.

The Critique of Pure Reason (German: Kritik der reinen Vernunft [1]) by Immanuel Kant, first published in 1781, second edition 1787, is one of the most influential works in the history of philosophy. Also referred to as Kant's "first critique," it was followed by the Critique of Practical Reason and the Critique of Judgement.

Before the time of Kant, it was generally held that whatever knowledge was a priori must be of the nature of an analytic judgment, that is, what is stated in the predicate must already be present in the subjet e. g. "An intelligent man is intelligent" or "An intelligent man is a man." In either case, the judgement is analytic because it is arrived at by analyzing the subject. Before the time of Kant, it was thought that all judgements of which we could be certain a priori were of this kind: that in all of them there was a predicate which was only part of the subject of which it was asserted. If this were so, we would be involved in a contradiction every time we would try to deny anything that could be known a priori e. g. "An intelligent man is not intelligent" or "An intelligent man is not a man." Thus according to the philosophers before Kant, the Law of contradiction is sufficient to establish all a priori knowledge. [1]


Kant's rejection of Hume's empiricism

Before Kant (1724-1804), David Hume (1711-1776) accepted the general view of rationalism about a priori knowledge. However, upon closer examination of the subject at hand, Hume discovered that some judgments considered to be analytical, specially those related to cause and effect, were in fact synthetical i. e. no analysis of the subject will reveal the predicate. Before Hume, rationalists held that effect could be deduced from cause; Hume argued that it could not and from this inferred that nothing at all could be known a priori in relation to cause and effect. Kant who was brought under the auspices of rationalism was deeply disturbed by Hume's skepticism. Kant decided to find an answer and spent ten years of meditation upon the subject.[2]

Kant's work was stimulated by taking seriously Hume's skeptical conclusions about such basic principles as cause and effect and the implications of this skepticism for Kant's grounding in rationalism. In Kant's view, Hume's skepticism rested on the premise that all ideas are presentations of sensory experience. The problem that Hume identified was that basic principles like causality cannot be derived from sense experience only: as Hume argued, we experience only that one event regularly succeeds another, not that it is caused by it. Kant's goal, then, was to find some way to derive cause and effect without relying on empirical knowledge. Kant rejects analytical methods for this, arguing that analytic reasoning can't tell us anything that isn't already self-evident (Bxvii). Instead, Kant argued that we would need to use synthetic reasoning. But this posed a new problem — how can one have synthetic knowledge that is not based on empirical observation — that is, how can we have synthetic a priori truths?

Immanuel Kant, lecturing to Russian officers — by I. Soyockina / V. Gracov, the Kant Museum, Kaliningrad

Kant argues that there are synthetic judgments such as the connexion of cause and effect where no analysis of the subject will produce the predicate. Kant reasones that statements such as those found in Geometry and Newtonian physics are synthetic judgments. Kant uses the classical example of 7 + 5 = 12. No amount of analysis will find 12 in either 7 or 5. Thus Kant arrives at the conclusion that all pure mathematics is synthetic though a priori; the number 7 is after all 7 and the number 5 is five and the number 12 is twelve and so on and so forth. For Kant then, Mathematics is synthetic judgement a priori. This conclusion led Kant into a new problem as he wanted to establish how this could be possible: How is pure mathematics possible?[3] This also led him to inquire whether it could be possible to ground synthetic a priori knowledge for a study of metaphysics, because most of the principles of metaphysics from Plato through to Kant's immediate predecessors made assertions about the world or about God or about the soul that were not self-evident but which could not be derived from empirical observation (B18-24). This led to his most influential contribution to metaphysics: the abandonment of the quest to try to know the world as it is "in itself" independent of our sense experience. He demonstrated this with a thought experiment, showing that we cannot meaningfully conceive of an object that exists outside of time and has no spatial components and isn't structured in accordance with the categories of the understanding, such as substance and causality. Although we cannot conceive of such an object, Kant argues, there is no way of showing that such an object does not exist. Therefore, Kant says, the science of metaphysics must not attempt to reach beyond the limits of possible experience but must discuss only those limits, thus furthering the understanding of ourselves as thinking beings.

"Since, then, the receptivity of the subject, its capacity to be affected by objects, must necessarily precede all intuitions of these objects, it can readily be understood how the form of all appearances can be given prior to all actual perceptions, and so exist in the mind a priori" (A26/B42). Appearance is then, via the faculty of transcendental imagination, grounded systematically in accordance with the categories of the understanding. Kant's metaphysical system, which focuses on the operations of cognitive faculties, places substantial limits on knowledge not founded in the forms of sensibility. Thus it locates the error of metaphysical systems prior to Critique in failing to first take into consideration the limitations of our human capacity for knowledge.

It is because of taking into account the role of our cognitive faculties in structuring the known and knowable world that in the second preface to the "Critique of Pure Reason" Kant compares his critical philosophy to Copernicus' revolution in astronomy. Kant writes: "Hitherto it has been assumed that all our knowledge must conform to objects. But all attempts to extend our knowledge of objects by establishing something in regard to them a priori, by means of concepts, have, on this assumption, ended in failure. 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" (Bxvi). Just as Copernicus revolutionized astronomy by changing the point of view and taking the position of the observer into account, Kant's critical philosophy takes into account the position of the knower of the world in general and reveals its impact on the structure of his/her known world.

Kant's transcendental idealism should be distinguished from idealistic systems such as Berkeley's. While Kant claimed that phenomena depend upon the conditions of sensibility, space and time, and on the synthesizing activity of the mind manifested in the rule-based structuring of perceptions into a world of objects, this thesis is not equivalent to mind-dependence in the sense of Berkeley's idealism. Kant defines transcendental idealism:

"I understand by the transcendental idealism of all appearances the doctrine that they are all together to be regarded as mere representations and not things in themselves, and accordingly that time and space are only sensible forms of our intuition, but not determinations given for themselves or conditions of objects as things in themselves. To this idealism is opposed transcendental realism, which regards space and time as something given in themselves (independent of our sensibility)." (CPR, A 369)

Kant's approach

In Kant's view, a priori intuitions and concepts provide us with some a priori knowledge, which also provides the framework for our a posteriori knowledge. Kant also believed that causality is a conceptual organizing principle that we impose upon nature, albeit nature understood as the sum of appearances that can be synthesized according to our a priori concepts.

In other words, space and time are a form of perceiving and causality is a form of knowing. Both space and time and our conceptual principles and processes pre-structure our experience.

Things as they are "in themselves" — the thing in itself or das Ding an sich — are unknowable. For something to become an object of knowledge, it must be experienced, and experience is structured by our minds—both space and time as the forms of our intuition or perception, and the unifying, structuring activity of our concepts. These aspects of mind turn things-in-themselves into the world of experience. We are never passive observers or knowers.

Kant's "I" — the "Transcendental Unity of Apperception" — is similarly unknowable. One is aware that there is an "I," a subject or self that accompanies one's experience and consciousness. Since one experiences it as it manifests itself in time, which Kant proposes is a subjective form of perception, one can know it only indirectly: as object, rather than subject.

The Critique of Pure Reason is arranged around several basic distinctions. After the two Prefaces (the A edition Preface of 1781 and the B edition Preface of 1787) and the Introduction, the book is divided into the Doctrine of Elements and the Doctrine of Method:

The Doctrine of Elements sets out the a priori products of the mind, and the correct and incorrect use of these presentations. Kant further divides the Doctrine of Elements into the Transcendental Aesthetic and the Transcendental Logic, reflecting his basic distinction between sensibility and the understanding. In the Transcendental Aesthetic he argues that space and time are pure forms of intuition inherent in our faculty of sense. The Transcendental Logic is separated into the Transcendental Analytic and the Transcendental Dialectic:

  • The Transcendental Analytic sets forth the appropriate uses of a priori concepts, called the categories, and other principles of the understanding, as conditions of the possibility of a science of metaphysics. The section titled the Metaphysical Deduction enucleates the origin of the categories. In the Transcendental Deduction, Kant then shows the application of the categories to experience. Next, the Analytic of Principles sets out arguments for the relation of the categories to metaphysical principles. This section begins with the Schematism, which describes how the imagination can apply pure concepts to the object given in sense perception. Next are arguments relating the a priori principles with the schematized categories.
  • The Transcendental Dialectic, describes the transcendental illusion behind the misuse of these principles in attempts to apply them to realms beyond sense experience. Kant’s most significant arguments are the Paralogisms of Pure Reason, the Antinomy of Pure Reason, and the Ideal of Pure Reason, aimed against, respectively, traditional theories of the soul, the universe as a whole, and the existence of God. In the Appendix to the Critique of Speculative Theology Kant describes the role of the transcendental ideas of reason.

The Doctrine of Method, contains four sections. The first section, Discipline of Pure Reason, compares mathematical and logical methods of proof, and the second section,Canon of Pure Reason, distinguishes theoretical from practical reason.

The Divisions of Critique of Pure Reason


1. First and second Prefaces
2. Introduction
3. Transcendental Doctrine of Elements
A. Transcendental Aesthetic
B. Transcendental Logic
(1) Transcendental Analytic
a. Analytic of Concepts
i. Metaphysical Deduction
ii. Transcendental Deduction
b. Analytic of Principles
i. Schematism (bridging chapter)
ii. System of Principles of Pure Understanding
a. Axioms of Intuition
b. Anticipations of Perception
c. Analogies of Experience
d. Postulates of Empirical Thought (Refutation of Idealism)
iii. Ground of Distinction of Objects into Phenomena and Noumena
iv. Appendix on the Amphiboly of the Concepts of Reflection
(2) Transcendental Dialectic: Transcendental Illusion
a. Paralogisms of Pure Reason
b. Antinomy of Pure Reason
c. Ideal of Pure Reason
d. Appendix to Critique of Speculative Theology
4. Transcendental Doctrine of Method
A. Discipline of Pure Reason
B. Canon of Pure Reason
C. Architectonic of Pure Reason
D. History of Pure Reason

I. Transcendental Doctrine of Elements


Transcendental Aesthetic[4]

Following Alexander Baumgarten, Kant held that there are two kinds of knowledge: sensible (sensual) and logical. Sensible knowledge is based on sensation; logical knowledge is based on reason. Kant's division of Transcendental Aesthetic and Transcendental Logic result from these two kinds of knowledge. The Transcendental Aesthetic is that part of the Critique of Pure Reason that considers the contribution of sensation to cognition.

Kant distinguished between the matter and the form of appearances. The matter is "that in the appearance which corresponds to sensation" (A20/B34). The form is "that which so determines the manifold of appearance that it allows of being ordered in certain relations" (A20/B34). Kant's revolutionary claim is that the form of appearances — which he later identifies as space and time — is a contribution made by the faculty of sensation to cognition, rather than something that exists independently of the mind. This is the thrust of Kant's doctrine of the transcendental ideality of space and time.

Kant's arguments for this conclusion are widely debated among Kant scholars. Some see the argument as based on Kant's conclusions that our representation of space and time is an a priori intuition. From here Kant is thought to argue that our representation of space and time as a priori intuitions entails that space and time are transcendentally ideal.[5] Others see the argument as based upon the question of whether synthetic a priori judgments are possible. Kant is taken to argue that the only way synthetic a priori judgments, such as those made in geometry, are possible is if space is transcendentally ideal.

Space and time

Kant gives two expositions of space and time: metaphysical and transcendental. The metaphysical expositions of space and time are concerned with clarifying how those intuitions are known independently of experience. The transcendental expositions attempt to show how the metaphysical conclusions might be applied to enrich our understanding.

In the transcendental exposition, Kant refers back to his metaphysical exposition in order to show that the sciences would be impossible if space and time were not kinds of pure a priori intuitions. He asks the reader to take the proposition, "two straight lines can neither contain any space nor, consequently, form a figure", and then to try to derive this proposition from the concepts of a straight line and the number two. He concludes that it is simply impossible (A47-48/B65). Thus, as we can't obtain this information from analytic reasoning; so it must be by way of synthetic reasoning, i.e., a synthesis of concepts (in this case two and straightness) with the pure (a priori) intuition of space.

But in this case, it wasn't experience that furnished the third term; otherwise, we would lose the necessary and universal character of geometry. Only space, which is a pure a priori form of intuition, can make this synthetic judgment, thus it must then be a priori. If geometry doesn't serve this pure a priori intuition, it is empirical, and would be an experimental science. But geometry doesn't proceed by measurements—it proceeds by demonstrations.

Kant rests his demonstration of the a priority of space on the example of geometry. He reasons that therefore if something exists, it needs to be intelligible. If we attacked this argument, we would doubt the universality of geometry (which no honest person would do, in Kant's estimation).

The other part of the Transcendental Aesthetic argues that time is a pure a priori intuition which renders mathematics possible. Time is not a concept, since otherwise it would merely conform to formal logical analysis (and therefore, to the principle of non-contradiction). However, time makes it possible to deviate from the principle of non-contradiction: indeed, it is possible to say that A and non-A are in the same spatial location if one considers them in different times, and a sufficient alteration between states were to occur (A32/B48). Time and space cannot thus be regarded as existing in themselves. They are a priori forms of sensible intuition.

The current interpretation of Kant states that the subject inherently possesses the underlying conditions to perceive spatial and temporal presentations. The Kantian thesis claims that in order for the subject to have any experience at all, then it must be bounded by these forms of presentations (Vorstellung). Some scholars have offered this position as an example of psychological nativism, as a rebuke to some aspects of classical empiricism.

Kant's thesis concerning the transcendental ideality of space and time limits appearances to the forms of sensibility—indeed, they form the limits within which these appearances can count as sensible; and it necessarily implies that the thing-in-itself is neither limited by them nor can it take the form of an appearance within us apart from the bounds of sensibility (A48-49/B66). Yet the thing-in-itself is held by Kant to be the cause of that which appears, and this is where the paradox of Kantian critique resides: while we are prohibited from absolute knowledge of the thing-in-itself, we can impute to it a cause beyond ourselves as a source of representations within us.

Transcendental Logic

In the Transcendental Logic, one finds a section (entitled the Refutation of Idealism) from Kant which frees his doctrine from any vestiges of subjective idealism which would either doubt or deny the existence of external objects (B274-79). Kant's distinction between the appearance and the thing-in-itself is not intended to imply that nothing knowable exists apart from consciousness, as with subjective idealism. Rather, it declares that knowledge is limited to phenomena as objects of a sensible intuition. In the Fourth Paralogism, Kant further certifies his philosophy as distinct from that of subjective idealism by defining his position as a transcendental idealism in accord with empirical realism (A366-80).

The Transcendental Logic is that part of the Critique where Kant investigates the understanding and its role in constituting our knowledge. The understanding is defined as the faculty of the mind which deals with concepts (A51-52/B75-76). The Logic is divided into two parts: the Analytic and the Dialectic. In the Analytic, Kant investigates the contributions of the understanding to knowledge. In the Dialectic, Kant investigates the limits of the understanding.

The idea of a transcendental logic is that of a logic which gives an account of the origins of our knowledge as well as its relationship to objects. This is contrasted by Kant with the idea of a general logic, which abstracts from the conditions under which our knowledge is acquired, and from any relation that knowledge has to objects.

Kant's investigation resulted in his claim that the real world of experience can only be an appearance or phenomenon. What things are in themselves, or, other than being appearances, are completely unknowable by any animal or human mind.

First Division: Transcendental Analytic

The Transcendental Analytic is divided into an Analytic of Concepts and an Analytic of Principles, as well as a third section concerned with the distinction between phenomena and noumena. The main sections of the Analytic of Concepts are The Metaphysical Deduction and The Transcendental Deduction of the Categories. The main sections of the Analytic of Principles are the Schematism, Axioms of Intuition, Anticipations of Perception, Analogies of Experience, Postulates and follow the same recurring tabular form:


Followed by the Refutation of Idealism (added in the 2nd edition).

The Metaphysical Deduction

Here Kant aims to derive the twelve pure concepts of the understanding (which he also calls "categories") from the logical forms of judgment. Kant arranges the forms of judgment in a table of judgments which he uses to guide the derivation of the table of categories.[6]

He creates a list of categories by first enumerating the forms of possible objective judgment which are endowed with their objectivity by virtue of their inherent a priori concepts. Kant claims that if we can identify all of the possible forms of objective judgment, we can then hope to use them as the basis to discover all of the most general concepts or categories that are employed in making such judgments, and thus that are employed in any cognition of objects.[6]

Now, the logicians have concerned themselves to ascertain and classify the various possible forms of logical judgments. Kant, without further inquiry, accepts and adopts, with one or two minor modifications, their work as correct and complete, and lays before his reader, accordingly, the following table of the different possible kinds or forms of logical judgments, reduced under four heads:

1.Quantity of Judgements

In each of these ‘moments’ of judgment, there are three alternative classifications;(A70/B95).

1.Quantity of Judgements
  • Universal
  • Particular
  • Singular
  • Affirmative
  • Negative
  • Infinite
  • Categorical
  • Hypothetical
  • Disjunctive
  • Problematic
  • Assertoric
  • Apodeictic

These Aristotelian ways of classifying judgments are the basis for his discerning the twelve correlated concepts of the understanding. Kant ultimately distinguishes twelve pure concepts of the understanding divided into four classes of three (A80/B106):

1.Categories of Quantity
  • Unity
  • Plurality
  • Totality
2.Categories of Quality
  • Reality
  • Negation
  • Limitation
3.Categories of Relation
  • Inherence and Subsistence (substance and accident)
  • Causality and Dependence (cause and effect)
  • Community (reciprocity between agent and patient)
4.Categories of Modality
  • Possibility—Impossibility
  • Existence—Non-existence
  • Necessity—Contingency

These categories, then, are the fundamental, primary, or native conceptions of the understanding, which flow from, or constitute the mechanism of, its nature, are inseparable from its activity, and are therefore, for human thought, universal and necessary, or a priori. They are not contingent states or images of sensuous consciousness, and hence not to be thence derived. But they are not known to us independently of such consciousness or of sensible experience. On the one hand, they are exclusively involved in, and hence come to our knowledge exclusively through, the spontaneous activity of the understanding. But, on the other hand, the understanding is never active, until sensible data are furnished as material for it to act upon, and so it may truly be said that they become known to us "only on the occasion of sensible experience."

These categories are "pure" conceptions of the understanding, in as much as they are independent of all that is contingent in sense. They are not derived from what is called the matter of sense, or from particular, variable sensations. But they are not independent of the universal and necessary form of sense. Again, Kant, in the "Transcendental Logic," is professedly engaged with the search for an answer to the second main question of the Critique, How is pure physical science, or sensible knowledge, possible? Kant, now, has said, and, with reference to the kind of knowledge mentioned in the foregoing question, has said truly, that thoughts, without the content which perception supplies, are empty. This is not less true of pure thoughts, than of any others. The content which the pure conceptions, as categories of pure physical science or sensible knowledge, cannot derive from the matter of sense, they must and do derive from its pure form. And in this relation between the pure conceptions of the understanding and their pure content there is involved, as we shall see, the most intimate community of nature and origin between sense, on its formal side (space and time), and the understanding itself.

The Transcendental Deduction

In the Transcendental Deduction, Kant aims to show that the categories derived in the Metaphysical Deduction are conditions of all possible experience. He achieves this proof by roughly the following line of thought: all representations must have some common ground if they are to be the source of possible knowledge (because extracting knowledge from experience requires the ability to compare and contrast representations that may occur at different times or in different places), this ground of all experience is the self-consciousness of the experiencing subject, and the constitution of the subject is such that all thought is rule-governed in accordance with the categories. It follows that the categories feature as necessary components in any possible experience.

1.Axioms of intuition
2.Anticipations of perception
3.Analogies of experience
4.Postulates of empirical thought in general
The Schematism

In order for any concept to have meaning, it must be related to sense perception. The 12 categories, or a priori concepts, are related to phenomenal appearances through schemata. Each category has a schema. It is a connection through time between the category, which is an a priori concept of the understanding, and a phenomenal a posteriori appearance. These schemata are needed to link the pure category to sensed phenomenal appearances because the categories are, as Kant says, completely heterogeneous with sense intuition.

The Refutation of Idealism

In order to answer criticisms of the Critique of Pure Reason that Transcendental Idealism denied the reality of external objects, Kant added a section to the second edition (1787) entitled "The Refutation of Idealism" that turns the "game" of idealism against itself by arguing that self-consciousness presupposes external objects in space. Defining self-consciousness as a determination of the self in time, Kant argues that all determinations of time presuppose something permanent in perception and that this permanence cannot be in the self, since it is only through the permanence that one's existence in time can itself be determined. This argument inverted the supposed priority of inner over outer experience that had dominated philosophies of mind and knowledge since Descartes.

Appendix: Amphiboly of Concepts of Reflection
"Through observation and analysis of appearances we penetrate to nature's inner recesses, and no one can say how far this knowledge may in time extend. But with all this knowledge, and even if the whole of nature were revealed to us, we should still never be able to answer those transcendental questions which go beyond nature. The reason of this is that it is not given to us to observe our own mind with any other intuition than that of inner sense; and that it is yet precisely in the mind that the secret of the source of our sensibility is located. The relation of sensibility to an object and what the transcendental ground of this [objective] unity may be, are matters undoubtedly so deeply concealed that we, who after all know even ourselves only through inner sense and therefore as appearance, can never be justified in treating sensibility as being a suitable instrument of investigation for discovering anything save always still other appearances -- eager as we yet are to explore their non-sensible cause." (A278/B334)

Second Division: Transcendental Dialectic

Following the systematic treatment of a priori knowledge given in the transcendental analytic, the transcendental dialectic seeks to dissect dialectical illusions. Its task is effectively to expose the fraudulence of non-empirical employment of the understanding. The Transcendental Dialectic shows how pure reason should not be used.

This longer but less dense section of the Critique is composed of five essential elements, as follows:

Introduction (to Reason and the Transcendental Ideas) Rational Psychology (the nature of the soul) Rational Cosmology (the nature of the world) Rational Theology (God) Appendix (on the constitutive and regulative uses of reason)

In the introduction, Kant introduces a new faculty, human reason, positing that it is a unifying faculty which unifies the manifold of knowledge gained by the understanding. Another way of thinking of reason is to say that it searches for the 'unconditioned'; Kant had shown in the Second Analogy that every empirical event has a cause, and thus each event is conditioned by something antecedent to it, which itself has its own condition, and so forth. Reason seeks to find an intellectual resting place which may bring the series of empirical conditions to a close, to obtain knowledge of an 'absolute totality' of conditions, thus becoming unconditioned.

The Paralogisms of Pure Reason

One of the ways that pure reason erroneously tries to operate beyond the limits of possible experience is when it thinks that there is an immortal Soul in every person. Its proofs, however, are paralogisms, or the results of false reasoning.

The Soul is substance

Every one of my thoughts and judgments is based on the presupposition "I think." "I" is the subject and the thoughts are the predicates. But I should not confuse the ever-present logical subject of my every thought with a permanent, immortal, real substance (soul). The logical subject is a mere idea, not a real substance.

The Soul is simple

The only use or advantage of asserting that the soul is simple is to differentiate it from matter and therefore prove that it is immortal. But the substratum of matter may also be simple. Since we know nothing of this substratum, both matter and soul may be fundamentally simple and therefore not different from each other. Then the soul may decay, as does matter. It makes no difference to say that the soul is simple and therefore immortal. Such a simple nature can never be known through experience. It has no objective validity.

The Soul is a person

In order to have coherent thoughts, I must have an "I" that is not changing and that thinks the changing thoughts. But we can't prove that there is a permanent soul or an undying "I" that constitutes my person. I only know that I am one person during the time that I am conscious. As a subject who observes my own experiences, I attribute a certain identity to myself. But, to another observing subject, I am an object of his experience. He may attribute a different persisting identity to me.

The Soul is separated from the experienced world

The soul is not separate from the world. They exist for us only in relation to each other. Whatever we know about the external world is only a direct, immediate, internal experience. The world appears, in the way that it appears, as a mental phenomenon. We cannot know the world as a thing-in-itself, that is, other than as an appearance within us. To think about the world as being totally separate from the soul is to think that a mere phenomenal appearance has independent existence outside of us. If we try to know an object as being other than an appearance, it can only be known as a phenomenal appearance, never otherwise. We cannot know a separate, thinking, non-material soul or a separate, non-thinking, material world because we cannot know things, as to what they may be by themselves, beyond being objects of our senses.

These Paralogisms cannot be proven for speculative reason and therefore can give no certain knowledge about the Soul. However, they can be retained as a guide to human behavior. In this way, they are necessary and sufficient for practical purposes. In order for humans to behave properly, they can suppose that the soul is an imperishable substance, it is indestructibly simple, it stays the same forever, and it is separate from the decaying material world.

The Antinomy of Pure Reason

The Ideas of Rational Cosmology are dialectical. They result in four kinds of opposing assertions, each of which is logically valid. The antinomy, with its resolution, is as follows:

Thesis: The world has, as to time and space, a beginning (limit). Antithesis: The world is, as to time and space, infinite. Both are false. The world is an object of experience. Neither statement is based on experience.

Thesis: Everything in the world consists of elements that are simple. Antithesis: There is no simple thing, but everything is composite. Both are false. Things are objects of experience. Neither statement is based on experience.

Thesis: There are in the world causes through freedom. Antithesis: There is no freedom, but all is nature. Both may be true. The thesis may be true of things-in-themselves (other than as they appear). The antithesis may be true of things as they appear.

Thesis: In the series of the world-causes there is some necessary being. Antithesis: There is nothing necessary in the world, but in this series all is contingent. Both may be true. The thesis may be true of things-in-themselves (other than as they appear). The antithesis may be true of things as they appear.

Pure Reason

Pure reason mistakenly goes beyond its relation to possible experience when it concludes that there is a Being who is the most real thing conceivable. This personified object is postulated by Reason as the subject of all predicates, the sum total of all reality. Kant called this Supreme Being, or God, the Ideal of Pure Reason because it exists as the highest and most complete condition of the possibility of all objects, their original cause and their continual support.

Ontological Proof of God's Existence

The Ontological Proof considers the concept of the most real Being and concludes that it is absolutely necessary. The Ontological Argument states that God exists because he is perfect. If he didn't exist, he would be less than perfect. Existence is assumed to be a predicate or attribute of the subject, God. But, Kant asserted that existence is not a predicate. Existence or Being is merely the infinitive of the copula or linking, connecting verb "is" in a declarative sentence. It connects the subject to a predicate. "Existence is evidently not a real predicate … The small word is, is not an additional predicate, but only serves to put the predicate in relation to the subject." (A599) Also, we cannot accept a mere concept or mental idea as being a real, external thing or object. The Ontological Argument starts with a mere mental concept of a perfect God and tries to end with a real, existing God.

Summarized further, we may say that this argument is essentially deductive in nature. Given a certain fact, it proceeds to infer another from it. The method pursued, then, is that of deducing the fact of God's being from the a priori idea of him. If man finds that the idea of God is necessarily involved in his self-consciousness, it is legitimate for him to proceed from this notion to the actual existence of the divine being. In other words, the idea of God necessarily includes existence. It may include it in several ways. One may argue, for instance, according to the method of Descartes, and say that the conception of God could have originated only with the divine being himself, therefore the idea possessed by us is based on the prior existence of God himself. Or we may allege that we have the idea that God is the most necessary of all beings — that is to say, he belongs to the class of realities; consequently it cannot but be a fact that he exists. This is held to be proof per saltum. A leap takes place from the premise to the conclusion, and all intermediate steps are omitted. The implication is that premise and conclusion stand over against one another without any obvious, much less necessary, connection. A jump is made from thought to reality. Kant here objects that being or existence is not a mere attribute which may be added on to a subject, thereby increasing its qualitative content. The predicate, being, adds something to the subject which no mere quality can give. It informs us that the idea is not a mere conception, but is also an actually existing reality. Being, as Kant thinks, actually increases the concept itself in such a way as to transform it. You may attach as many attributes as you please to a concept; you do not thereby lift it out of the subjective sphere and render it actual. So you may pile attribute upon attribute on the conception of God, but at the end of the day you are not necessarily one step nearer his actual existence. So that when we say God exists, we do not simply attach a new attribute to our conception; we do far more than this implies. We pass our bare concept from the sphere of inner subjectivity to that of actuality. This is the great vice of the Ontological argument. The idea of ten dollars is different from the fact only in reality. In the same way the conception of God is different from the fact of his existence only in reality. When, accordingly, the Ontological proof declares that the latter is involved in the former, it puts forward nothing more than a mere statement. No proof is forthcoming precisely where proof is most required. We are not in a position to say that the idea of God includes existence, because it is of the very nature of ideas not to include existence.

Cosmological ("Prime Mover") Proof of God's Existence

The Cosmological Proof considers the concept of an absolutely necessary Being and concludes that it has the most reality. In this way, the Cosmological Proof is merely the converse of the Ontological Proof. But the Cosmological Proof purports to start from sense experience. It says, "If anything exists in the cosmos, then there must be an absolutely necessary Being. " It then claims that there is only one concept of an absolutely necessary object. That is the concept of a Supreme Being who has maximum reality. Only such a supremely real being would be necessary and independently sufficient without compare. But this is the Ontological Proof again, which was asserted a priori without sense experience.

Summarizing The Cosmological Argument further, it may be stated as follows: Contingent things exist — at least I exist; and as they are not self-caused, nor capable of explanation as an infinite series, it is requisite to infer that a necessary being, on whom they depend, exists. Seeing that this being exists, he belongs to the realm of reality. Seeing that all things issue from him, he is the most necessary of beings, for only a being who is self-dependent, who possesses all the conditions of reality within himself, could be the origin of contingent things. And such a being is God. This proof is invalid for three chief reasons. First, it makes use of a category, namely, Cause. And, as has been already pointed out, it is not possible to apply this, or any other, category except to the matter given by sense under the general conditions of space and time. If, then, we employ it in relation to Deity, we try to force its application in a sphere where it is useless, and incapable of affording any information. Once more, we are in the now familiar difficulty of the paralogism of Rational Psychology or of the Antinomies. The category has meaning only when applied to phenomena. But God is a noumenon. Second, it mistakes an idea of absolute necessity — an idea which is nothing more than an ideal — for a synthesis of elements in the phenomenal world or world of experience. This necessity is not an object of knowledge, derived from sensation and set in shape by the operation of categories. It cannot be regarded as more than an inference. Yet the cosmological argument treats it as if it were an object of knowledge exactly on the same level as perception of any thing or object in the course of experience. Thirdly, it presupposes the Ontological argument, already proved false. It does this, because it proceeds from the conception of the necessity of a certain being to the fact of his existence. And it is possible to take this course only if idea and fact are convertible with one another. It has just been proved that they are not so convertible.

Physico-theological ("Watch Maker") Proof of God's Existence

The Physico-theological Proof of God's existence is supposed to be based on a posteriori sensed experience of nature and not on mere a priori abstract concepts. It observes that the objects in the world have been intentionally arranged with great wisdom. The fitness of this arrangement could never have occurred randomly, without purpose. The world must have been caused by an intelligent power. The unity of the relation between all of the parts of the world leads us to infer that there is only one cause of everything. That one cause is a perfect, mighty, wise, and self-sufficient Being. This physico-theology does not, however, prove with certainty the existence of God. For this, we need something absolutely necessary that consequently has all-embracing reality. But this is the Cosmological Proof, which concludes that an all-encompassing real Being has absolutely necessary existence. All three proofs can be reduced to the Ontological Proof, which tried to make an objective reality out of a subjective concept.

II. Transcendental Doctrine of Method

The second book in the Critique, and by far the shorter of the two, attempts to lay out the formal conditions of the complete system of pure reason.

In the Transcendental Dialectic, Kant showed how pure reason is improperly used when it is not related to experience. In the Method of Transcendentalism, he explained the proper use of pure reason.

The Discipline of Pure Reason

Discipline is the restraint, through caution and self-examination, that prevents philosophical pure reason from applying itself beyond the limits of possible sensual experience. Philosophy cannot possess dogmatic certainty. Philosophy, unlike mathematics, cannot have definitions, axioms or demonstrations. All philosophical concepts must be ultimately based on a posteriori, experienced intuition. This is different from algebra and geometry, which use concepts that are derived from a priori intuitions, such as symbolic equations and spatial figures.

Restraint should be exercised in the polemical use of pure reason. Kant defined this polemical use as the defense against dogmatic negations. For example, if it is dogmatically affirmed that God exists or that the soul is immortal, a dogmatic negation could be made that God doesn't exist or that the soul is not immortal. Such dogmatic assertions can't be proved. The statements are not based on possible experience.

Kant claimed that adversaries should be freely allowed to speak reason. In return, they should be opposed through reason. Dialectical strife leads to an increase of reason's knowledge. But there ought to be no dogmatic polemical use of reason. The critique of pure reason is the tribunal for all of reason's disputes. It determines the rights of reason in general. We should be able to openly express our thoughts and doubts. This leads to improved insight. We should eliminate polemic in the form of opposed dogmatic assertions that cannot be related to possible experience.

According to Kant, the censorship of reason is the examination and possible rebuke of reason. Such censorship leads to doubt and skepticism. After dogmatism produces opposing assertions, skepticism usually occurs. The doubts of skepticism awaken reason from its dogmatism and bring about an examination of reason's rights and limits. It is necessary to take the next step after dogmatism and skepticism. This is the step to criticism. By criticism, the limits of our knowledge are proved from principles, not from mere personal experience.

If criticism of reason teaches us that we can't know anything unrelated to experience, can we have hypotheses, guesses, or opinions about such matters? We can only imagine a thing that would be a possible object of experience. The hypotheses of God or a soul cannot be dogmatically affirmed or denied. But we have a practical interest in their existence. It is therefore up to an opponent to prove that they don't exist. Such hypotheses can be used to expose the pretensions of dogmatism.

Proofs of transcendental propositions about pure reason (God, soul, free will, causality, simplicity) must first prove whether the concept is valid. Reason should be moderated and not asked to perform beyond its power. The three rules of the proofs of pure reason are: (1) consider the legitimacy of your principles, (2) each proposition can have only one proof because it is based on one concept and its general object, and (3) only direct proofs can be used, never indirect proofs (e.g., a proposition is true because its opposite is false). By attempting to directly prove transcendental assertions, it will become clear that pure reason can gain no speculative knowledge and must restrict itself to practical, moral principles.

The Canon of Pure Reason

The speculative propositions of God, immortal soul, and free will have no cognitive use but are valuable to our moral interest. In pure philosophy, reason is morally (practically) concerned with what ought to be done if the will is free, if there is a God, and if there is a future world. But, in its actual practical employment and use, reason is only concerned with the existence of God and a future life.

The greatest advantage of the philosophy of pure reason is negative, the prevention of error. But moral reason can provide positive knowledge. There can't be a canon, or system of a priori principles, for the correct use of speculative reason. However, there can be a canon for the practical (moral) use of reason.
Reason has three main questions and answers:

  1. What can I know? We cannot know, through reason, anything that can't be a possible sense experience;
  2. What should I do? Do that which will make you deserve happiness;
  3. What may I hope? We can hope to be happy as far as we have made ourselves deserving of it through our conduct.

Reason tells us that there is a God, the supreme good, who arranges a future life in a moral world. If not, moral laws would be idle fantasies. Our happiness in that intelligible world will exactly depend on how we have made ourselves worthy of being happy. The union of speculative and practical reason occurs when we see God's reason and purpose in nature's unity of design or general system of ends.

In the transcendental use of reason, there can be neither opinion nor knowledge. Reason results in a strong belief in the unity of design and purpose in nature. This unity requires a wise God who provides a future life for the human soul. Such a strong belief rests on moral certainty, not logical certainty. Even if a person has no moral beliefs, the fear of God and a future life acts as a deterrent to evil acts, because no one can prove the non-existence of God and an afterlife. Does all of this philosophy merely lead to two articles of faith, namely, God and the immortal soul? With regard to these essential interests of human nature, the highest philosophy can achieve no more than the guidance which belongs to the commonest understanding.

The Architectonic of Pure Reason

All knowledge from pure reason is architectonic in that it is a systematic unity. The entire system of metaphysic consists of: (1.) Ontology – objects in general; (2.) Rational Physiology – given objects; (3.) Rational cosmology – the whole world; (4.) Rational Theology - God. Metaphysic supports religion and curbs the extravagant use of reason beyond possible experience. The components of metaphysic are criticism, metaphysic of nature, and metaphysic of morals. These constitute philosophy in the genuine sense of the word. It uses science to gain wisdom. Metaphysic investigates reason, which is the foundation of science. Its censorship of reason promotes order and harmony in science and maintains metaphysic's main purpose, which is general happiness.

The History of Pure Reason

Metaphysics began with the study of the knowledge of God and the nature of a future world. It was concluded early that good conduct would result in happiness in another world as arranged by God. The object of rational knowledge was investigated by sensualists (Epicurus), and intellectualists (Plato). Sensualists claimed that only the objects of the senses are real. Intellectualists asserted that true objects are known only by the understanding mind. Aristotle and Locke thought that the pure concepts of reason are derived only from experience. Plato and Leibniz contended that they come from reason, not sense experience, which is illusory. Epicurus never speculated beyond the limits of experience. Locke, however, said that the existence of God and the immortality of the soul could be proven. Those who follow the naturalistic method of studying the problems of pure reason use their common, sound, or healthy reason, not scientific speculation. Others, who use the scientific method, are either dogmatists (Wolff) or skeptics (Hume). All of the above methods are faulty. The method of criticism remains as the path toward the completely satisfying answers to the metaphysical questions about God and the future life in another world.

Terms and phrases

Intuition and concept

Kant distinguishes between two different fundamental types of representation: intuitions and concepts.

  1. Concepts are "mediate representations" (see A68/B93). Mediate representations represent things by representing general characteristics of things. For example, consider a particular chair. The concepts "brown," "wooden," "chair," and so forth are, according to Kant, mediate representations of the chair. They can represent the chair by representing general characteristics of the chair: being brown, being wooden, being a chair, and so forth.
  2. Intuitions are "immediate representations" (see B41), that is, representations that represent things directly. One's perception of the chair is, according to Kant, an immediate representation. The perception represents the chair directly, and not by means of any general characteristics.

Kant divides intuitions in the following ways:

  1. Kant distinguishes intuitions into pure intuitions and empirical intuitions. Empirical intuitions are intuitions that contain sensation. Pure intuitions are intuitions that do not contain any sensation (A50/B74). An example of an empirical intuition would be one's perception of a chair or another physical object. All such intuitions are immediate representations that have sensation as part of the content of the representation. The pure intuitions are, according to Kant, those of space and time, which are our mind's subjective condition of coordinating sensibilia. Our representations of space and time are not objective and real, but immediate representations that do not include sensation within those representations. Thus both are pure intuitions.
  2. Kant also divides intuitions into two groups in another way. Some intuitions require the presence of their object, i.e. of the thing represented by the intuition. Other intuitions do not. (The best source for these distinctions is Kant's Lectures on Metaphysics.) We might think of these in non-Kantian terms as first, perceptions, and second, imaginations (see B151). An example of the former: one's perception of a chair. An example of the latter: one's memory of a chair that has subsequently been destroyed. Throughout the Transcendental Aesthetic, Kant seems to restrict his discussion to intuitions of the former type: intuitions that require the presence of their object.

Kant also distinguised between a prior (pure) and a posteriori (empirical) concepts.

"A Critique Of Pure Reason" was also the name of a popular entertainment student radio programme on Cambridge University Radio (CUR1350).

English Translations of Kritik der reinen Vernunft

  • Francis Haywood (1838) (First English translation)
  • J.M.D. Meiklejohn (1855)
  • Friedrich Max Müller (1881)
  • Norman Kemp Smith (1929)
  • Wolfgang Schwartz (Concise Text, 1982)
  • Werner S. Pluhar (1996)
  • Paul Guyer and Allen Wood (Cambridge University Press, February, 1999)
  • Marcus Weigelt (Penguin Books, 2007)

Secondary sources

  • Martin Heidegger, Kant and the Problem of Metaphysics 5th ed. trans. Richard Taft. Indiana University Press: Bloomington (1973).
  • Arthur Schopenhauer, The World as Will and Representation, Volume I, Appendix "Criticism of the Kantian Philosophy", Dover, ISBN 0-486-21761-2
  • Bennett, J., Kant's Analytic (1966)
  • Bennett, J., Kant's Dialectic (1974)
  • Cassirer, H., Kant's first critique (1954)
  • Ewing, A. C., A short commentary on Kant's Critique of Pure Reason (1938)
  • Palmquist, Stephen, Kant's System of Perspectives (1993)
  • Paton, H. J., THE METAPHYSICS OF EXPERIENCE, 2 vols. (1936)
  • Strawson, P. F., THE BOUNDS OF SENSE (1966)
  • Ameriks, K., KANT'S THEORY OF MIND (1982)
  • Beck, L. W., ESSAYS ON KANT AND HUME (1978)
  • Bencivenza, E., KANT'S COPERNICAN REVOLUTION (1987)
  • Broad, C. D., KANT: AN INTRODUCTION (1978)
  • Buchdahl, G., KANT AND THE DYNAMICS OF REASON (1992)
  • de Vleeschauwer, H. J., THE DEVELOPMENT OF KANT'S THOUGHT (1962)
  • Gram, M. S., INTERPRETING KANT (1982)
  • Gram, M. S., KANT, ONTOLOGY, AND THE A PRIORI (1968)
  • Hartnack, J., KANT'S THEORY OF KNOWLEDGE (1967)
  • Melnick, A., SPACE, TIME AND THOUGHT IN KANT (1989)
  • Nagel, Gordon, THE STRUCTURE OF EXPERIENCE (1983)
  • Prichard, H.A., KANT'S THEORY OF KNOWLEDGE (1909)
  • Seung, T. K., KANT: A GUIDE FOR THE PERPLEXED (2007)
  • Smith, A. H., KANTIAN STUDIES (1947)
  • Waxman, W., KANT'S MODEL OF THE MIND (1991)
  • Wood, A. W., KANT'S RATIONAL THEOLOGY (1978)

See also


  1. ^ Russell, Bertrand (2008). The Problems of Philosophy. Arc Manor LLC. pp. 56-57. ISBN 1604500851. 
  2. ^ Bertrand Russell. The Problems of Philosophy. p. 57. 
  3. ^ Bertrand Russell. The Problems of Philosophy. p. 57. 
  4. ^ "Aesthetic" here means sensation, and not art theory as it is now used.
  5. ^ see Henry Allison, "Kant's Transcendental Idealism"
  6. ^ a b Immanuel Kant, Critique of Pure Reason, trans. and ed. by Paul Guyer and Allen W. Wood, Cambridge Univ. Press, 1998, pp. 8-9 (translators' introduction).

Further reading

Other Major Works by Kant

  • Thoughts on the True Estimation of Living Forces 1746
  • On Fire [Doctoral Dissertation] 1755
  • A New Explanation of the First Principles of Metaphysical Knowledge [Habilitation] 1755
  • General Natural History and Theory of the Heavens 1755
  • Physical Monadology 1756
  • New Theory of Motion and Rest 1758
  • Some Experimental Reflections about Optimism 1759
  • The False Subtlety of the Four Syllogistic Figures Demonstrated 1762
  • Enquiry into the Clarity of the Principles of Natural Theology and Morality 1762, 1764
  • On the Only Possible Argument for Proving the Existence of God 1763
  • Attempt to Introduce the Concept of Negative Quantitites into Philosophy 1763
  • Observations on the Feeling of the Beautiful and Sublime 1764
  • Dreams of a Visionary, Explained by Dreams of Metaphysics 1766
  • The First Ground of the Distinction of Regions in Space 1768
  • On the Form and Principles of the Sensible and the Intelligible World [Inaugural Dissertation] 1770
  • Prolegomena to Any Future Metaphysics 1783
  • Idea for a Universal History 1784
  • What is Enlightenment? 1784
  • Foundations of the Metaphysics of Morals 1785
  • Metaphysical Foundations of Natural Science 1786
  • Conjectural Beginning of Human History 1786
  • Critique of Practical Reason 1788
  • Critique of Judgment 1790, 1793
  • Religion Within the Limits of Reason Alone 1793, 1794
  • The End of All Things 1794
  • Perpetual Peace 1795, 1796
  • The Metaphysics of Morals 1797, 1798-1803
  • The Strife of the Faculties 1798
  • Anthropology from a Pragmatic Point of View 1798
  • Logic 1800


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