The Immanuel Kant's Critique of Pure Reason

Take a journey through Immanuel Kant's masterpiece, the Critique of Pure Reason. Understand Kant's revolutionary system of thought and its implications on modern philosophy.

 In the eighteenth century, the century of Enlightenment, it was between those two philosophies that a thinking person had to choose. It was Kant’s principal contribution to show that the choice between empiricism and rationalism is unreal, that each philosophy is equally mistaken, and that the only conceivable metaphysics that could commend itself to a reasonable being must be both empiricist and rationalist at once.

Immanuel Kant's Critique of Pure Reason is one of the most influential works in modern philosophical thought. This monumental work revolutionized understanding of metaphysical concepts like causality, existence, and freedom, providing a path towards understanding reality, human nature, and morality.

Causality: How Are Events Caused? 

One of Kant's central arguments in The Critique of Pure Reason is that causality is necessary for the orderly structure of experience. He believes that we must presuppose a causal chain of events in order to make sense of our experience. Without this chain, phenomena would appear random and chaotic. To maintain its validity, he argued that such certainty can only be determined by pure reason. In other words, our understanding of causality does not come from observation or empirical evidence but from an innate capacity for reasoning about cause and effect relationships.

What is the Relationship Between Knowledge and Reason ?

Kant argued that knowledge is determined by reason, not by experience. He asserted that experience can give us information, but true knowledge of the world comes from our innate capacity to reason—specifically, the capacity to use pure a priori concepts and judgments. This means that when we are trying to understand and make sense of reality, we must draw on the resources of pure reason rather than relying on our senses.

Overview of Immanuel Kant's Life and Work. 

Immanuel Kant (1724–1804) lived and taught at Königsberg, then in Prussia (but now part of Russia). He studied philosophy and eventually went on to become a professor at the University of Konigsberg, where he lectured for over twenty years. During this time, he wrote his famous work, the Critique of Pure Reason. Published in 1781, this work outlined Kant's system of thought which helped form the basis of modern philosophical systems and paved the way for many developments since. 

Kant early works (known as the ‘precritical’ writings) were followed by a period of silence (1770–1781) and then by the first of the three great Critiques—the Critique of Pure Reason (1781, second edition 1787). This dealt in a systematic way with the entire field of epistemology and metaphysics; it was followed by the Critique of Practical Reason (1788), concerned with ethics, and the Critique of Judgement (1790), concerned largely with aesthetics. Among Kant’s other works, the most important are the Prolegomena to any Future Metaphysics (1783) and The Foundation of the Metaphysic of Morals (1785), the first being a popular exposition of his mature metaphysics, the second of his lifelong stance towards morality. His writings on logic, jurisprudence and political philosophy have been less influential, although Hegel’s political transformation of the Critique of Practical Reason has had an incalculable effect on subsequent political thought and practice.

Of diminutive stature and austere habits, Kant was nevertheless a gregarious man, a brilliant talker, and a loved and respected member of social and literary circles. He was a founding spirit of the German Romantic movement which was to change the consciousness of Europe, and also the father of nineteenth-century idealism. He was (and remains) the greatest philosopher since Aristotle, and his most important book— the Critique of Pure Reason—is of an intellectual depth and grandeur that defy description. Mme de Staël wrote of it thus:

"Immanuel Kant treatise on the nature of the human understanding, entitled the ‘Examination of Pure Reason’, appeared nearly thirty years ago, and this work was for some time unknown; but when at length the treasures of thought which it contains were discovered, it produced such a sensation in Germany, that almost all which has been accomplished since in literature as well as in philosophy, has flowed from the impulse given by this performance I shall devote this article a discussion of that work, leaving the ethics, the aesthetics and the vagaries of Kant’s immediate influence to the chapter which follows."

Historical Context and Introduction to the Critique of Pure Reason. 

The Critique of Pure Reason was originally written by Kant as a response to what he saw as the essential shortcomings of contemporary, mainly rationalist, philosophy. He believed that these philosophies were too focused on theorizing and not grounded in experience. As such, Kant set out to provide an empirical basis for philosophical inquiry, thereby establishing a system of thought that emphasized understanding the nature of reality through experience. In doing so, he argued for a new approach to philosophy, which provided the foundation for modern philosophical systems and helped pave the way for many subsequent developments in philosophy since his time.

Introducing Kant's Critical Philosophy

Immanuel Kant's Critique of Pure Reason marked a major turning point in the history of modern philosophy. Through his groundbreaking philosophical system, Kant offered substantial critiques of rationalism and empiricism at the time and proposed an entirely unique approach to metaphysics. By drawing from his own peculiar concept of transcendental idealism, Kant sought to uncover an ultimate form of knowledge in which both experience-based and rationalist thinking could be unified. At the heart of Kant's method was his belief that all phenomena are part of a greater, holistic system that is yet to be fully comprehended.

Kant’s early philosophical inspiration had been the system of Leibniz, as expounded by Wolff . But despite this influence—which is everywhere apparent in the Critique of Pure Reason—Kant’s philosophy is unique, both in its methods and in its aims. In order to understand those aims we must again consider the impact, during the seventeenth and eighteenth centuries, of the rise of science. Science presented itself as a universal discipline, the premises of which were certain, and the methods of which were disputable only by the adoption of a stance of philosophical scepticism. No one could engage in science without accepting both the established results of his predecessors, and also the empirical methods that led to their discovery. 

Science presented a picture of unanimity and objectivity which no system of metaphysics could rival. Forced by this fact into unnatural self-consciousness, philosophy found itself with no results that it could offer as its own peculiar contribution to the fund of human knowledge. The very possibility of metaphysics was thrown in doubt, and this doubt was only exacerbated by Hume’s radical scepticism—a scepticism which, according to Kant, aroused him from his ‘dogmatic [by which he meant Leibnizian] slumbers’. All philosophy, then, for Kant, must begin from the question ‘How is metaphysics possible?’

In answer to that question, Kant attempted a systematic critique of human thought and reason. He tried to explore not just scientific beliefs, but all beliefs, in order to establish exactly what is presupposed in the act of belief as such. He wished to describe the nature and limits of knowledge, not just in respect of scientific discovery, but absolutely: his metaphysics was designed, not as a postscript to physics, but as the very foundation of discursive thought. He hoped to show three things:

1 That there is a legitimate employment of the understanding, the rules of which can be laid bare, and that limits can be set to this legitimate employment. (It is a striking conclusion of Kant’s thought that rational theology is not just unbelievable, but unthinkable.)

2 That Humean scepticism is impossible, since the rules of the understanding are already sufficient to establish the existence of an objective world obedient to a law of causal connection.

3 That certain fundamental principles of science—such as the principle of the conservation of substance, the principle that every event has a cause, the principle that objects exist in space and time, can be established a priori.

Kant’s proof of these contentions begins from the theory of ‘synthetic a priori’ knowledge. According to Kant, scientific knowledge is a posteriori: it arises from, and is based in, actual experience. Science, therefore, deals not with necessary truths but with matters of contingent fact. However, it rests upon certain universal axioms and principles, which, because their truth is presupposed at the start of any empirical enquiry, cannot themselves be empirically proved. These axioms are, therefore, a priori, and while some of them are ‘analytic’ (true by virtue of the meanings of the words used to formulate them), others are ‘synthetic’, saying something substantial about the empirical world.

Moreover, these synthetic a priori truths, since they cannot be established empirically, are justifiable, if at all, through reflection, and reflection will confer on them the only kind of truth that is within its gift: necessary truth. They must be true in any conceivable world. 

Kant's Theory of Synthetic Judgments.

Synthetic judgments are those which expand our knowledge beyond the information provided in the subject and predicate of a statement. Kant hypothesized that synthetic judgments are always true for any object that falls within the scope of the judgment, even if this truth is not necessarily experienced or observable. Kant saw mathematics and geometry as demonstrations of synthetic truths, as theorems necessarily follow from certain axioms regardless of whether they can be seen in reality. This led to Kant’s further exploration not only into theoretical philosophy but natural science and empirical inquiry as well.

The original question of metaphysics has become: ‘How is synthetic a priori knowledge possible?’

Kant compared his answer to that question (to which he gave the vivid name ‘transcendental idealism’) to the Copernican revolution in astronomy, because, like Copernicus, he had moved away from the narrow vision which sees one thing as central, towards a wider vision from which that one thing (in this case the capacities of the human understanding) can be surveyed and criticised. There is an immediate intellectual difficulty of which Kant was aware, and which provides the explanation of the word ‘transcendental’ (a technical term which has as little to do with ‘Transcendental Meditation’ as with Liszt’s Transcendental Studies).

Synthetic a Priori Knowledge and Antinomies of Pure Reason.

Immanuel Kant was also a key proponent of the idea of synthetic a priori knowledge, which states that certain truths can be known independently of experience and yet still rely on it. He used this concept to bridge the gulf between experience-based and rationalist approaches to philosophy, and he highlighted its essential importance for legitimizing philosophical inquiry. Additionally, Kant dealt with the antinomies of pure reason, which argue for contradictory assertions about reality and the nature of time, space, substance, and causality. By looking at these antinomies from a unified perspective based in empirical observation, Kant developed his own synthesis to address them and helped shift philosophy away from one-sided theorizing.

Judgment - A- priori and A – posterior

The Latin phrases a-priori ('from the earlier') and a-posteriori ('from the later') are philosophical terms popularized by Immanuel Kant's Critique of Pure Reason (first published in 1781, second edition in 1787), one of the most influential works in the history of philosophy. However, in their Latin forms they appear in Latin translations of Euclid's Elements, of about 300 BC, a work widely considered during the early European modern period as the model for precise thinking.

These terms are used with respect to reasoning (epistemology) to distinguish "necessary conclusions from first premises" (i.e., what must come before sense observation) from "conclusions based on sense observation" which must follow it. Thus, the two kinds of knowledge, justification, or argument, may be glossed:

• A-priori knowledge or justification is independent of experience, as with mathematics (3 + 2 = 5), tautologies ("All bachelors are unmarried"), and deduction from pure reason (e.g., ontological proofs).

• A-posteriori knowledge or justification depends on experience or empirical evidence, as with most aspects of science and personal knowledge.

There are many points of view on these two types of knowledge, and their relationship gives rise to one of the oldest problems in modern philosophy.

The terms a-priori and a-posteriori are primarily used as adjectives to modify the noun "knowledge" (for example, "a priori knowledge"). However, "a priori" is sometimes used to modify other nouns, such as "truth". Philosophers also may use "apriority" and "aprioricity" as nouns to refer (approximately) to the quality of being "a priori".

Although definitions and use of the terms have varied in the history of philosophy, they have consistently labeled two separate epistemological notions. See also the related distinctions: deductive/inductive, analytic/synthetic, necessary/contingent. The intuitive distinction between a priori and a posteriori knowledge (or justification) is best seen via examples, as below:

A-priori -Consider the proposition: "If Mehul V reigned at least four days, then he reigned more than three days". This is something that one knows a-priori, because it expresses a statement that one can derive by reason alone.

A-posteriori - Compare this with the proposition expressed by the sentence: "Mehul V reigned from 1910 to 1936". This is something that (if true) one must come to know a-posteriori, because it expresses an empirical fact unknowable by reason alone.

The 18th-century German philosopher Immanuel Kant (1781) advocated a blend of rationalist and empiricist theories. Kant says, "Although all our cognition begins with experience, it does not follow that it arises [is caused by] from experience"

Transcendental Idealism and the Critique of Judgment.

Since Kant's aim was to develop a philosophical system that acknowledged both experience-based and rationalist approaches, his ideas about transcendental idealism took center stage within the Critique of Pure Reason. Transcendental idealism is Kant's notion that reality can never be fully understood from the perspective of pure reason, since humans only observe phenomena through the veil of time, space, and causality. Thus, this notion asserts that certain concepts beyond empirical evidence – such as freedom, immortality and God – must always remain outside of knowledge. In his subsequent work on epistemology in the Critique of Judgment, Kant further clarified his position by introducing principles for what makes something worthy of being called an authentic concept or idea.

Kant's transcendental method

Analogously, if the synthetic a priori principles of the understanding are as fundamental to thought as Kant asserted, then the very attempt to establish their validity must at the same time assume them. It was for this reason that Kant called his philosophical method ‘transcendental’, since it contained an attempt to transcend through argument what argument must presuppose. Not surprisingly, the possibility of such ‘transcendental argument’ has been the object of continual scepticism. Nevertheless, the individual conclusions of the Critique of Pure Reason are of such interest, and often of such intrinsic plausibility, that Kant’s own theory as to the nature of his method has dissuaded only the most fatuously common sensical from trying to reconstruct his argument Kant believed that neither the empiricists nor the rationalists could provide a coherent theory of knowledge. 

The first, who elevate experience over understanding, deprive themselves of the concepts with which experience might be described (for no concept can be derived as a mere ‘abstraction’ from experience); while the second, who emphasise understanding at the expense of experience, deprive themselves of the very subject matter of knowledge. Knowledge is achieved through a synthesis of concept and experience, and Kant called this synthesis ‘transcendental’, meaning that it could never be observed as a process, but must always be presupposed as a result. Synthetic a priori knowledge is possible because we can establish that experience, if it is to be subject to this synthesis, must conform to the ‘categories’ of the understanding.

Kant's categories of understanding

These categories are the basic forms of thought, or a priori concepts, under which all merely empirical concepts are subsumed. (For example, the concept ‘table’ is subsumed under ‘artifact’, which in turn is subsumed under ‘object’ and hence under ‘substance’; the concept of ‘killing’ is subsumed under ‘action’, which falls under ‘cause’. The categories are the end-points of these chains of subsumption, points beyond which one cannot proceed, since they represent the most basic operations of human thought.) Thus we can know a priori that our world (if it is to be our world) must obey certain principles, principles implicit in such concepts as substance, object and cause, and that it must fall under the general order of space and time.

The Transcendental Deduction of the Categories

The cornerstone of this anti-sceptical proof occurs in a famous, but extremely obscure, passage of the Critique of Pure Reason, known as ‘The Transcendental Deduction of the Categories’. This exists in two versions, corresponding to the two editions of the "Critique of Pure Reason", and it is hard to say which version is to be preferred, since neither is fully intelligible. But the outline of the argument can be displayed, and it can be seen that, if valid, it is one of the most important arguments in the whole of philosophy.

Like Descartes, Kant begins from an examination of an aspect of self consciousness. But, unlike Descartes, he uses his arguments in order to reject what I have called ‘the priority of the first person’. In other words, he removes the privileges from subjectivity, and in doing so destroys the possibility of an empiricist theory of the mind. The immediate result is that epistemology becomes secondary to metaphysics; for without metaphysics the deliverances of the senses become impossible to describe Kant’s near contemporary Lichtenberg remarked that Descartes should have said not, ‘I think’, but only, ‘It thinks in me’. 

However, as Kant recognised, there is contained in the idea of a thought, as of every mental content, the notion of a subject. Moreover, this subject has an immediate and intuitive apprehension of its own unity: I know immediately of my present mental states that they are mine, and in the normal case I cannot be wrong about this. (In other words, in the case of the present contents of the mind, the distinction between being and seeming evaporates. This is what is meant by the ‘subjectivity’ of the first person.) It is impossible that I should be in the position of Mrs Gandhi (in Hard Times), who, on her deathbed, knew only that there was a pain in the room somewhere, but not that it was hers. Nor do I have to find out that my pain and my thought belong to a single consciousness. My having these states presupposes my ability to assign them to the single subjective unity of the self.

Kant refers to this unity as the ‘Transcendental Unity of Apperception’, ‘apperception’ meaning self-consciousness, and the word ‘transcendental’ indicating that the ‘unity’ of the self is not known as the conclusion of an argument but as the presupposition of all self-knowledge. Now this unity is not a mere ‘binding force’ among mental items; it is what Kant calls an ‘original’ unity. It consists, in other words, in the existence of a thing (the subject), which bears its mental states not as adjuncts but as properties. 

The very idea of self-knowledge leads us therefore to the unity of the self, as an entity over and above the totality of its mental contents. It follows that there is more to the self than present self knowledge can offer. The self has an identity (and in particular, an identity through time) beyond the mere collection of its present thoughts and feelings. Hence, while I may have immediate knowledge of my present mental states, there are other aspects of myself about which I might be mistaken, and about which I might have to find out. I might have to discover the truth about my past and future.

 Hence the self as subject presupposes the self as object. While there is an area of self-knowledge which is subjective (where the distinction between being and seeming evaporates), this is possible only because the self has an enduring, objective identity, in other words, only because it may also be other than it seems. So a subject of experience, if it is to have knowledge of itself as subject, must inhabit an objective world, a world in which the general concept of an object finds application. Radical scepticism, which can be stated only from the premise of self-knowledge, therefore presupposes its own falsehood.

According to Kant, the Transcendental Deduction establishes the validity (in some sense) of the general concept of objectivity. It remains to discover what that concept contains, and it is here that we must turn again to the theory of the categories. Kant argues that all knowledge involves the application of concepts to experience. Having shown that no knowledge is possible, not even self-knowledge, without the general concept of an object, we can at once conclude that experience must conform to the strictures which that concept contains. 

In other words, experience must conform to the categories; for these are nothing more than a working out in detail of all that is contained in the abstract concept of objectivity. Thus I cannot think in terms of objects without thinking of entities that endure through change; this requires that I apply to my experience the concept of substance. But substance, in its turn, involves the idea of something that sustains itself in being, and that idea involves the notion of causality (or causal explanation). Causality in turn requires the idea of a law of nature, and hence the notions of necessity, possibility and actuality. And so on. Thus we see that, from the assumption that experience falls under the concept of an object, we arrive at the conclusion that it must fall under all the categories in turn.

There is a further step in Kant’s argument. For, having shown (as he thinks) that experience conforms to the categories, he feels that he must show that the categories conform to experience. That is, they cannot denote mere abstractions, but must have their primary application in experience; and that means (as he argues at the very beginning of the Critique) in space and time. (Kant’s thesis in the first section—the Transcendental Aesthetic—is that space is the ‘form’ of ‘outer sense’, time is the ‘form’ of ‘inner sense’. This means, roughly, that the idea of experience is inseparable from that of time, and the idea of an experienced world is inseparable from that of space.) In this way, he tries to show that the rationalist view of knowledge is as mistaken as the empiricist view. For rationalism assumes an understanding of such categories as cause and substance independently of any actual or possible experience to which they might be applied. 

Through the process of ‘fit’ between concept and experience, Kant argues, the whole of scientific knowledge is generated. And it is through examining the structure of this ‘fit’ that the synthetic a priori principles of the understanding may be expounded and justified. For example, if we are to understand how it is that the category of cause gains application in experience, we must see experience itself as already restricted by a general principle of causality, the principle that every event has a cause. By elaborating the system of ‘principles’ Kant hoped to establish that the fundamental axioms of science are synthetic a priori. In this, while he was partly influenced by the parochial conceptions of Newtonian physics and Euclidean geometry, he was also able to argue in abstraction from those sciences, and to deliver results which might well be accepted by many contemporary scientists. For example, Kant attempted to provide a proof of the unity of science (the theory of all events as falling under a law of mutual influence), of the necessity of a principle of conservation of ‘substance’ (mass for example, or energy), of the need for both intensive and extensive magnitudes in the formulation of scientific laws. All these proofs carry persuasive weight beyond the limitations implicit in eighteenth-century scientific thought.

Kant refutation of idealism

What does Kant mean in referring to his philosophy as a form of ‘idealism’ (albeit ‘transcendental’)? This is one of the most puzzling questions of Kantian exegesis, in particular since Kant expressly dismisses the philosophy of Berkeley (which he labels ‘empirical idealism’), asserts that ‘transcendental idealism’ is a form of ‘empirical realism’, and appends to the second edition of the Critique a chapter called ‘The Refutation of Idealism’. First, however, it is necessary to grasp Kant’s important distinction between ‘phenomenon’ and ‘noumenon’. Kant’s theory of the synthetic a priori depends crucially upon the element of empiricism in his philosophy—the view that knowledge comes through the synthesis of concept and ‘intuition’. 

We can have a priori knowledge of reality only as ‘phenomenon’—as a possible object of empirical observation. Phenomena are those things which can be discovered to be thus and thus; things, in other words, which enter into causal relation with ourselves and our experience. Philosophers like Leibniz had tried to describe reality as ‘noumenon’—as the object of pure intellectual apprehension. Kant’s theory of the synthetic a priori and his refutation of scepticism are meant to establish the reality of the phenomenal world (the ‘world of appearance’). To try to establish the reality of the noumenal world is to attempt to achieve knowledge by pure concepts alone; it is to attempt to transcend the limits of the human understanding and so achieve knowledge of a world that could never be empirically discovered. Such an attempt involves the transformation of understanding into ‘pure reason’, and Kant regarded it as doomed to failure. Part of the meaning of the phrase ‘transcendental idealism’ is contained, then, in this robust emphasis on the empirical as the legitimate sphere of knowledge, and on the impossibility of knowing a ‘noumenon’ or ‘thing-in-itself.

Kant transcendental idealism

But does Kant’s ‘transcendental idealism’ really contain a refutation of scepticism? 

There is a systematic ambiguity in the actual theory of transcendental idealism which makes it difficult to answer this question. The ambiguity is contained in the phrase, used in the last paragraph: ‘the world of appearance’.  The world is a ‘world of appearance’ only in the sense that it exists in time, consisting of objects and processes which are either perceived by us, or else causally related to our perception. One might call this the ‘objective’ interpretation of Kant’s theory. It is an interpretation that makes the theory incompatible with Humean scepticism.

However, there is a rival interpretation, which we might call ‘subjective’. Until recently this was far more widely accepted, despite being compatible at least with the intentions underlying the Humean point of view. This rival interpretation emphasises not ‘empirical realism’ but ‘transcendental idealism’. It interprets the Transcendental Deduction as expounding a thesis about the nature of the human mind. It is our finite capacities that are being described, and the attack on empiricism is directed, not against scepticism, but against the impoverished concept of human mentality (and in particular the untenable concept of ‘experience’) from which empiricism departs. When Kant says that we have knowledge not of the world ‘as it is in itself’, but only of the world as it appears (‘the world of appearance’), this could be read as a complicated way of agreeing with the empiricist’s conclusions. The world of appearance marks a limit which we cannot in the nature of things transcend. Knowledge is described in subjective terms—as something generated by the understanding, through the synthesis of concept and intuition. In no sense does it, on this interpretation, reach beyond that synthesis to an independent world (the world of the ‘thing-in-itself’).

This rival psychologistic interpretation of Kant can find support in the text, and has been profoundly influential. In retrospect, however, it seems to me that only the objective interpretation of the first Critique allows us to think of Kant’s enterprise as either worthwhile or significant.

Kant's critique of pure reason

In the second part of the Critique of Pure Reason Kant diagnoses the failure of ‘pure reason’, trying to show that the attempt to employ concepts outside the limits prescribed by their empirical application leads inevitably to fallacies—in the form of paradoxes, incoherencies and direct contradictions. The inevitable tendency of reason to transcend the limits of intelligibility Kant called the ‘Dialectic’ of reason (and this concept was to have a profound influence—through Hegel—on subsequent philosophy, although an influence that was at variance with Kant’s intentions). Kant tried to show that all the traditional metaphysical (specifically rationalist) arguments—arguments about the substantiality and immortality of the soul, the infinitude of the universe, the necessary existence of God and the reality of free will—were inevitably grounded in contradiction and paradox. The brilliance of his exposition of these errors, together with the fascination of his diagnosis of them, not as accidental but as inevitable diseases of the understanding, are unsurpassed in the history of philosophy. There is space, however, to mention only the most important of Kant’s conclusions, those concerning the soul and God. The account of free will must await the article which follows.

Kant’s view of the soul is extremely subtle. He begins once again from the notion of ‘apperception’. It is clear that there is no thought without a subject. And because that subject must have privileged access to its present mental states it is tempting to think, with Descartes, that its pure ‘subjectivity’ provides some indication of its essential nature; that the abolition of the distinction between being and seeming licenses the inference to the conclusion that the self has a purely ‘subjective’ being; hence that the self is not subject to the laws of objects, being indestructible and indivisible. Kant points out that there is a fallacy in this inference. There is no passage from the privilege of self-knowledge to the essence of what is known. The privilege of the first person presupposes the existence of the self as object; it is therefore not for self knowledge to determine what it knows. The essence of the self remains hidden, even though its accidents are immediately ‘given’ to consciousness. Kant goes on to connect this view with a theory of practical knowledge, and of the moral being of the self.

Just as the understanding has its categories, so does ‘pure reason’ have its ‘ideas’. These are categories that have outrun, as it were, the possibility of cognitive application—permanent delusions of the understanding, which one is constrained always to pursue but never to grasp. Among these ideas is that of infinity, construed not as indefiniteness (as in the perpetual incompletion of a mathematical series) but as a completed infinity (as in the Platonic and Boethian view of time). The principal and most compelling instance of that idea is God, and it is to the refutation of the traditional arguments for God’s existence that Kant turned his attention in much of the Dialectic. In particular, he presented a famous refutation of the ontological argument, a refutation which a great many have chosen to regard as conclusive, and also as damaging to the whole enterprise of rational theology. The argument turns on the premise that existence is not a predicate; it is therefore impossible, Kant argued, to advance from the concept of God to the existence of God.

No concept can imply its own instantiation, and the logical character of existence is misrepresented by any attempt to make it part of the concept of a thing. Kant’s premise contained a premonition of one of the most important results of modern logic. This result was to change the course of philosophy once again.

Kant’s dismissal of the claims of ‘pure reason’ was subject to certain important reservations. For one thing, he regarded the ‘ideas’ of reason as having an important ‘regulative’ function. If regarded, not as autonomous instruments of knowledge, but as signposts for the understanding, their theoretical employment would lead not to error, but to the constant stimulation of fresh discovery. There was a more important use of ‘pure reason’, however, adumbrated already in parts of the Dialectic, but fully elaborated only in the Critique of Practical Reason. Reason finds its legitimate employment in the practical sphere, and we can understand the claims of theology, for example, if we see them, not as intellectual truths which could be stated and argued for, but, so to speak, as ‘intimations’, made manifest to our consciousness when we act in obedience to the moral law.

Summary Kant's Critique of Pure Reason

Kant's Critique of Pure Reason is a cornerstone of modern Western philosophy and explores the notion that the human mind is the filter through which all experience must pass. Kant posits that our capacity for reasoning gives us access to a priori concepts such as space, time and causality, allowing us to make judgments about phenomena rooted in experience. 

Kant's Critique of Pure Reason contains three discourses that make up the Transcendental Deduction. The first discourse aims to show that all human knowledge involves reference to a priori concepts such as space and time, while the second examines how human beings interpret experience with these conceptual tools. Finally, the third discourse takes it a step further by exploring how humans use the categories of understanding, such as causation and substance, to form judgments about reality. In short, Kant's discourses are an examination of how we make sense of our world and explore the limits of reason.

The Critique of Pure Reason features two connected volumes that explore the concept of ‘pure reason’. Kant's main goal was to probe more deeply into how human cognition organizes and interprets experience, leading him to theorize about a priori knowledge. He develops an analysis which rests upon his distinction between analytic and synthetic statements as well as between rationalism and empiricism. Ultimately, Kant concludes that neither side alone can provide sufficient answers and that a synthesis is required between both elements is necessary for full understanding.

Impact and Significance on Contemporary Thought.

Kant's Critique of Pure Reason continues to have an immense impact on contemporary thought. His concept of transcendental idealism has inspired various other thinkers in various fields, from mathematics to linguistics. The Critique of Pure Reason also gave birth to Kant’s “Copernican turn” of philosophy; it marks the beginning of modern philosophical inquiry, as Kant shifted away from centuries-old metaphysical speculation and towards more rigorous exploration of the human mind. From the influence on existentialists such as Jean-Paul Sartre, to even mechanical engineers, Kant's writings are a pervasive force throughout today's intellectual landscape.

Immanuel Kant critique of pure reason quotes

Respect. Every man is to be respected as an absolute end in himself; and it is a crime against the dignity that belongs to him as a human being, to use him as a mere means for some external purpose. - Kant famous quotes

• “I had to deny knowledge in order to make room for faith.”
•  “All our knowledge begins with the senses, proceeds then to the understanding, and ends with reason. There is nothing higher than reason.”
•  “Whereas the beautiful is limited, the sublime is limitless, so that the mind in the presence of the sublime, attempting to imagine what it cannot, has pain in the failure but pleasure in contemplating the immensity of the attempt”
•  “Thoughts without content are empty, intuitions without concepts are blind.”
•  “Man must be disciplined, for he is by nature raw and wild..”
• “Skepticism is thus a resting-place for human reason, where it can reflect upon its dogmatic wanderings and make survey of the region in which it finds itself, so that for the future it may be able to choose its path with more certainty. But it is no dwelling-place for permanent settlement. Such can be obtained only through perfect certainty in our knowledge, alike of the objects themselves and of the limits within which all our knowledge of objects is enclosed.”
•  “The light dove, in free flight cutting through the air the resistance of which it feels, could get the idea that it could do even better in airless space. Likewise, Plato abandoned the world of the senses because it posed so many hindrances for the understanding, and dared to go beyond it on the wings of the ideas, in the empty space of pure understanding.”
•  “it was the duty of philosophy to destroy the illusions which had their origin in misconceptions, whatever darling hopes and valued expectations may be ruined by its explanations.”
•  “Two things fill the mind with renewed and increasing awe and reverence the more often and the more steadily that they are meditated on: the starry skies above me and the moral law inside me. I have not to search for them and conjecture them as though they were veiled in darkness or were in the transcendent region beyond my horizon; I see them before me and connect them directly with the consciousness of my existence”
•  “all human cognition begins with intuitions, proceeds from thence to conceptions, and ends with ideas.”
•  “The schematicism by which our understanding deals with the phenomenal world ... is a skill so deeply hidden in the human soul that we shall hardly guess the secret trick that Nature here employs.”
• “It is the Land of Truth (enchanted name!), surrounded by a wide and stormy ocean, the true home of illusion, where many a fog bank and ice, that soon melts away, tempt us to believe in new lands, while constantly deceiving the adventurous mariner with vain hopes, and involving him in adventures which he can never leave, yet never bring to an end.”
•  “Human reason, in one sphere of its cognition, is called upon to consider questions, which it cannot decline, as they are presented by its own nature, but which it cannot answer, as they transcend every faculty of the mind.”
•  “Our age is the age of criticism, to which everything must be subjected. The sacredness of religion, and the authority of legislation, are by many regarded as grounds of exemption from the examination of this tribunal. But, if they on they are exempted, they become the subjects of just suspicion, and cannot lay claim to sincere respect, which reason accords only to that which has stood the test of a free and public examination.]”
•  “But, above all, it will confer an inestimable benefit on morality and religion, by showing that all the objections urged against them may be silenced for ever by the Socratic method, that is to say, by proving the ignorance of the objector.”
• “Every beginning is in time, and every limit of extension in space. Space and time, however, exist in the world of sense only. Hence phenomena are only limited in the world conditionally, the world itself, however, is limited neither conditionally nor unconditionally.”
•  “Metaphysics... is nothing but the inventory of all we possess through pure reason, ordered systematically. Nothing here can escape us, because what reason brings forth entirely out of itself cannot be hidden, but is brought to light by reason itself as soon as reason's common principle has been discovered. The perfect unity of this kind of cognition, and the fact that it arises solely out of pure concepts without any influence that would extend or increase it from experience or even particular intuition, which would lead to a determinate experience, make this unconditioned completeness not only feasible but also necessary. Tecum habita, et noris quam sit tibi curta supellex. Dwell in your own house, and you will know how simple your possessions are. - Persius”
• “never wish to see a just cause defended with unjust means”
• “Deficiency in judgement is properly that which is called stupidity; and for such a failing we know no remedy. A dull or narrow-minded person, to whom nothing is wanting but a proper degree of understanding, may be improved by tuition, even so far as to deserve the epithet of learned. But as such persons frequently labour under a deficiency in the faculty of judgement, it is not uncommon to find men extremely learned who in the application of their science betray a lamentable degree this irremediable want.]”
• “For if the question is absurd in itself and demands unnecessary answers, then, besides the embarrassment of the one who proposes it, it also has the disadvantage of misleading the incautious listener into absurd answers, and presenting the ridiculous sight (as the ancients said) of one person milking a billy-goat while the other holds a sieve underneath. (A58/B82)”
•  “The great mass of people are worthy of our respect.”
• “Experience may teach us what is, but never that it cannot be otherwise.”
• “To know what questions may reasonably be asked is already a great and necessary proof of sagacity and insight. For if a question is absurd in itself and calls for unnecessary answers, it not only brings disgrace to the person raising it, but may prompt an incautious listener to give absurd answers, thus presenting, as the ancients said, the laughable spectacle of one person milking a he-goat, and another holding the sieve underneath.”
• “Philosophical knowledge is knowledge which reason gains from concepts; mathematical knowledge is knowledge which reason gains from the construction of concepts.”
• “(On the seeming futility of metaphysics) Why then has nature afflicted our reason with the restless striving for such a path, as if it were one of reason's most important occupations? Still more, how little cause have we to place trust in our reason if in one of the most important parts of our desire for knowledge it does not merely forsake us but even entices us with delusions and in the end betrays us! Or if the path has merely eluded us so far, what indications may we use that might lead us to hope that in renewed attempts we will be luckier than those who have gone before us?”
•  “...by saying that the former was only concerned with quality, the latter only with quantity, mistook cause for effect.”