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Immanuel Kant

What Other Thinkers Have Said About Kant

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What Other Thinkers Have Said About Kant

A Gallery of Admiration, Criticism, and Intellectual Response

Immanuel Kant (1724–1804) stands at one of the great crossroads in the history of philosophy. Few philosophers have provoked such a remarkable combination of admiration, resistance, correction, and transformation. Fichte, Schelling, Hegel, Schopenhauer, Nietzsche, Kierkegaard, Heidegger, Russell, and many others could not simply ignore Kant. Even when they rejected important parts of his philosophy, they usually did so while responding to questions Kant had made newly unavoidable.

The following collection is therefore not intended to establish whether Kant was "right." It is a record of how major thinkers encountered him.

1. Arthur Schopenhauer (1788–1860)

Schopenhauer may have been Kant's most passionate admirer among the major post-Kantian philosophers—and simultaneously one of his most severe critics.

Schopenhauer regarded Kant as the indispensable starting point for serious modern philosophy.

"The effect of these works on a mind to which they truly speak is ... comparable to a cataract operation on a blind person."

Schopenhauer, The World as Will and Representation, Supplement to Book I.

He continued:

"The principal works of Kant" are "the most important phenomenon to emerge in philosophy over the past two thousand years."

This is extraordinary praise. Schopenhauer believed Kant had fundamentally altered the philosophical understanding of the world. Yet he immediately added that serious study of Kant had enabled him to discover "significant errors" which had to be separated from what was true and excellent in Kant's system.

Schopenhauer especially valued Kant's distinction between phenomenon and thing-in-itself. He thought Kant had discovered something decisive: the world as experienced is inseparable from the subject experiencing it.

"Kant exhibited these laws, and therefore the whole world, as conditioned by the form of knowledge belonging to the subject."

Schopenhauer's own philosophy then attempted to go beyond Kant by asking what lies behind the world as representation.

He regarded Kant's discovery as a doorway—but believed Kant stopped at the doorway.

Schopenhauer's striking metaphor

Schopenhauer compared Kant's achievement to discovering that one cannot simply keep traveling horizontally in order to escape the world:

"Kant then circumnavigated the world and showed that, because it is round, one cannot get out of it by horizontal movement."

His proposed alternative was profoundly different:

"We must seek the end and beginning of the world, not without, but within us."

Schopenhauer's criticism of Kant's language

Schopenhauer admired Kant's intellectual power but was considerably less charitable about Kant's prose:

"Kant's language is often indistinct, indefinite, inadequate, and sometimes obscure."

He nevertheless attributed some of this obscurity to the extraordinary difficulty of Kant's subject matter.

Schopenhauer's verdict: Kant opened the door to modern metaphysics; Schopenhauer believed he could walk through it.

2. Georg Wilhelm Friedrich Hegel (1770–1831)

Hegel's relationship with Kant is one of the most important intellectual relationships in modern philosophy.

Hegel regarded Kant as a decisive breakthrough, but thought Kant had not carried his own critical project far enough.

Hegel recognized the revolutionary character of Kant's question: before confidently claiming knowledge of reality, philosophy must investigate the powers and limitations of knowledge itself.

Yet Hegel objected that Kant's philosophy retained too sharp a distinction between the knowing subject and the object known.

Hegel wrote:

"The step taken by Kant is a great and important one."

But he immediately questioned Kant's procedure of examining the instrument of knowledge before using it:

"It is the old story of the who would not go into the water till he could swim."

Hegel's objection was that examining reason is itself an exercise of reason. We cannot somehow step outside thought in order to inspect thought from an entirely neutral position.

This became one of Hegel's fundamental objections to Kant.

Hegel's great debt to Kant

Despite his criticism, Hegel regarded Kant's achievement as enormous.

Kant had made knowledge itself an object of philosophical investigation.

Hegel called this:

"a great and important" step.

Hegel's project can therefore be understood partly as an attempt to continue Kant's revolution while removing what Hegel considered Kant's remaining dualisms.

Where Kant asked:

What can reason legitimately know?

Hegel increasingly asked:

Can reason, by following its own development, overcome the boundary Kant placed before it?

Modern scholarship emphasizes that Hegel's criticism is not simply a rejection of Kant. Hegel retained Kant's conviction that philosophy must understand the boundaries and activity of reason, even while giving that activity a much more expansive role.

Hegel's verdict: Kant began the self-criticism of reason; Hegel believed reason could go farther than Kant allowed.

3. Johann Gottlieb Fichte (1762–1814)

Fichte was among the first great philosophers to attempt to build a new philosophy directly out of Kant.

For Fichte, Kant's decisive insight was that philosophy could not simply begin with an independently existing world of objects. It had to reckon with the activity of the subject.

Fichte therefore transformed Kant's transcendental subject into the active I.

The crucial movement was:

Kant: What are the conditions that make experience possible?

Fichte: What is the activity of the self that makes experience possible?

Fichte thus moved toward a philosophy in which the self is not merely a passive recipient of experience but an active principle.

William James later summarized the Fichtean transformation memorably:

"The real thing in itself, according to Fichte, is the active I, the Ego, the subject of self-consciousness."

James added:

"We and our world exist together."

And then:

"Our world is the expression of our character."

This represents a major development beyond Kant. The Kantian subject becomes, in Fichte, an active principle of reality rather than merely the formal condition under which experience is organized.

Fichte's verdict: Kant discovered the central role of the subject; Fichte sought to make the active self the foundation of philosophy.

4. Friedrich Wilhelm Joseph Schelling (1775–1854)

Schelling inherited Kant's critical philosophy but became increasingly dissatisfied with what he regarded as its inability to reach the deeper ground of being.

One important insight remained Kantian:

"the unconditioned ground of being which reason needs cannot be shown by reason itself to exist."

But Schelling pushed toward a question Kant had deliberately restricted:

What is the reality that precedes conceptual thought?

Schelling increasingly emphasized the primacy of being over the conceptual structures through which the mind attempts to comprehend it.

A striking description of the dissatisfaction that developed within post-Kantian philosophy is Schelling's image of philosophy as:

"a preface to which the book is still missing"

and

"an ever-rattling mill which however is unable to bring forth the bread of life."

The criticism is revealing: philosophy can construct increasingly elaborate conceptual machinery while still failing to reach being itself.

Schelling's verdict: Kant revealed the limits of conceptual reason, but the reality lying beyond those concepts remained philosophically urgent.

5. Johann Wolfgang von Goethe (1749–1832)

Goethe's response to Kant is particularly fascinating because Goethe approached reality through nature, perception, imagination, artistic experience, and direct encounter, rather than primarily through transcendental analysis.

Goethe was attracted to aspects of Kant's Critique of Judgment, especially its treatment of aesthetic experience. But he did not accept the Kantian framework wholesale.

The contrast between Goethe and Kant can be put simply:

Kant: What are the conditions under which experience of nature is possible?

Goethe: What does nature reveal when we learn to observe it correctly?

Goethe's approach was therefore much more phenomenological and experiential.

The Goethe-Lexicon notes that Goethe was able to salvage elements of Kant's critical philosophy while incorporating them into his own intellectual project.

A later interpretation by Rudolf Steiner described the difference starkly:

"Goethe's way of thinking" and Kant's philosophy represented "exactly the opposite pole."

Goethe's attraction to Kant was therefore selective. He found important insights in Kant's aesthetics without accepting Kant's entire theory of knowledge.

Goethe's verdict: Kant's investigation of judgment and aesthetics was fruitful, but nature could not be reduced to the structures imposed upon experience by the knowing subject.

6. Friedrich Heinrich Jacobi (1743–1819)

Jacobi was one of the earliest and most important critics of Kant's transcendental idealism.

His objection went directly to the problem of the thing-in-itself.

If the thing-in-itself is genuinely beyond possible experience, Jacobi asked, how can Kant legitimately assert that it exists or that it causes our sensations?

The problem can be expressed very simply:

If we cannot know the thing-in-itself, on what grounds can we say that it causes what we experience?

This criticism became one of the central problems inherited by post-Kantian philosophy.

The same difficulty was later emphasized by G. E. Schulze: it appears incoherent to claim philosophical knowledge of a mind-independent object that lies beyond all possible experience while simultaneously maintaining that such an object causes our sensory experience.

Jacobi's verdict: Kant's philosophy seemed to require the very metaphysical reality that his own critical method had placed beyond knowledge.

7. G. E. Schulze (1761–1833)

Schulze intensified the challenge.

His Aenesidemus (1792) attacked the foundations of the Kantian system indirectly through its defenders, especially Karl Leonhard Reinhold.

The central objection was devastatingly simple:

If Kant says that we cannot know things-in-themselves, how can he legitimately make claims about things-in-themselves?

Schulze thereby helped force post-Kantian philosophers to confront a problem that would dominate German philosophy for decades.

Schulze's verdict: Kant's critical philosophy had not completely escaped the metaphysics it claimed to have overcome.

8. Heinrich Heine (1797–1856)

Heine understood Kant not merely as an academic philosopher but as a revolutionary intellectual force.

His description of Kant is wonderfully dramatic.

Heine compared Kant's intellectual significance with the French Revolution and Robespierre.

He wrote that Robespierre had killed a king and thousands of Frenchmen, whereas Kant had:

"killed God"

by undermining traditional philosophical arguments for theology.

Heine then observed the astonishing contrast between Kant's quiet personal life and the revolutionary implications of his thought.

Had the people of Königsberg understood the significance of Kant's philosophy, Heine suggested, they might have regarded him with something like the fear inspired by an executioner.

Instead, they saw only:

"a professor of philosophy"

and casually greeted him as he passed by.

Heine's portrait captures something essential about Kant:

the exterior man was extraordinarily orderly; the intellectual consequences of his philosophy were revolutionary.

Heine's verdict: The quiet professor of Königsberg was intellectually more explosive than he appeared.

9. Friedrich Nietzsche (1844–1900)

Nietzsche's relationship with Kant was complicated.

He inherited Kant's suspicion of naïve metaphysics but rejected Kant's confidence that reason could provide a universal, objective moral law in the form Kant proposed.

Nietzsche regarded Kantian morality as another manifestation of the tendency to turn historically developed human values into apparently timeless necessities.

The deepest Nietzschean challenge to Kant therefore concerns the status of morality.

Kant asks:

What moral law must every rational being recognize?

Nietzsche asks:

Who created this moral law, and what human needs produced it?

The difference is enormous.

For Kant, morality expresses rational universality.

For Nietzsche, moral systems themselves become objects of psychological and genealogical investigation.

Thus Nietzsche's philosophy can be understood partly as an attempt to reverse Kant's direction of inquiry: rather than beginning with the universal conditions of rational morality, Nietzsche asks about the historical, psychological, physiological, and cultural forces that generated particular moral systems.

Nietzsche's verdict: Kant's supposedly universal moral reason may conceal historical and psychological origins that reason itself does not recognize.

10. Søren Kierkegaard (1813–1855)

Kierkegaard shared Kant's insistence that human beings cannot simply live by detached theoretical knowledge.

But Kierkegaard thought Kant's philosophy remained too deeply invested in universal rational structures.

Kierkegaard's central concern was the existing individual.

Kant asks:

What must rational beings do?

Kierkegaard increasingly asks:

What does this particular human being actually choose, become, and live?

This is a crucial transition from universal ethics to existential existence.

Kant's moral philosophy emphasizes duty.

Kierkegaard emphasizes inwardness, commitment, choice, faith, and the transformation of the individual.

The two therefore meet on the seriousness of moral life but diverge sharply over the nature of the individual's relationship to universal rational law.

Kierkegaard's verdict: The universal moral subject of philosophy is not yet the concrete individual who must actually live.

11. Arthur Schopenhauer on Kantian Morality

Schopenhauer's criticism of Kant's ethics deserves separate treatment because he believed Kant had constructed morality too formally.

Kant's categorical imperative attempts to determine whether a maxim can be universalized.

Schopenhauer objected that this turns morality into a matter of abstract rational form.

He attacked Kant's conception of the human being as an end in himself, arguing that the formulation was conceptually problematic.

Schopenhauer wanted morality grounded not in abstract rational law but in compassion.

Thus:

Kant: morality begins with rational obligation.

Schopenhauer: morality begins with the direct recognition of another's suffering.

This is one of the great alternative paths that emerged from the Kantian revolution.

12. Bertrand Russell (1872–1970)

Russell admired Kant's importance but rejected major portions of Kant's theory of knowledge.

One of Russell's central objections concerned Kant's account of a priori knowledge.

Russell argued that Kant's solution:

"unduly limits the scope of a priori propositions"

while failing to explain adequately why we can be certain of logical and mathematical truths.

Russell's alternative was to move toward a Platonic conception of universals and logical truth.

This represents an important shift:

Kant: the structure of experience is partly determined by the knowing subject.

Russell: at least some logical and mathematical truths possess a reality that cannot simply be explained as structures imposed by human cognition.

Russell's verdict: Kant asked the right question about a priori knowledge but gave the wrong account of its source.

13. Peter Strawson (1919–2006)

Strawson's The Bounds of Sense (1966) represents one of the most important twentieth-century attempts to recover Kant's enduring philosophical achievements while rejecting parts of his transcendental idealism.

Strawson believed that Kant had uncovered extraordinarily important truths about the conditions required for objective experience and judgment.

But he attempted to separate those insights from Kant's stronger metaphysical commitments.

One of Strawson's descriptions of a particular Kantian argument is famously severe:

"a non sequitur of numbing grossness"

Yet Strawson's overall project was not simply destructive.

He believed that important Kantian arguments could survive even after Kant's transcendental idealism was rejected.

This is an especially interesting pattern in the history of philosophy:

Keep Kant's questions. Keep some of Kant's arguments. Remove some of Kant's metaphysics.

Strawson's verdict: Kant's analysis of the conditions of objective experience contains lasting philosophical discoveries even if his transcendental idealism does not survive intact.

14. Martin Heidegger (1889–1976)

Heidegger regarded Kant as a crucial figure in the history of the question of Being.

Rather than treating Kant merely as an epistemologist, Heidegger attempted to uncover the deeper ontological implications of the Critique of Pure Reason.

Kant's analysis of time, imagination, and the unity of experience became particularly important to Heidegger.

Heidegger's interpretation therefore asks whether Kant came closer to a philosophy of Being than Kant himself realized.

In Heidegger's reading, Kant's investigation into the conditions of experience points toward something deeper:

What is the temporal structure of the human being that makes experience possible at all?

Heidegger therefore regarded the Kantian project as an important precursor to fundamental ontology.

A recurring Kantian formulation that became significant for Heidegger concerns the role of the understanding in structuring nature:

"The understanding is itself the lawgiver of nature."

Heidegger used Kant's formulation to explore the relationship between subjectivity, world, and the conditions under which beings can appear as intelligible.

Heidegger's verdict: Kant's critique of knowledge conceals a deeper investigation into the structure of human existence and Being.

15. Ernst Cassirer (1874–1945)

Cassirer represented another major twentieth-century approach to Kant.

For Cassirer, Kant was not merely the philosopher who erected barriers between the human mind and reality. Kant represented the beginning of a much broader philosophy of human symbolic activity.

Science, mathematics, language, art, myth, and culture could all be understood as ways in which human beings construct meaningful forms of experience.

Cassirer therefore helped transform Kant's transcendental philosophy into a philosophy of culture.

The movement is:

Kant: What are the conditions that make experience possible?

Cassirer: What symbolic forms make human culture and knowledge possible?

This makes Kant a starting point for a much broader philosophical anthropology.

16. Karl Barth (1886–1968)

Barth's relationship with Kant is particularly important for theology.

Kant's critical philosophy placed powerful restrictions upon what theoretical reason could establish about God.

For theology, this created both a challenge and an opportunity.

If God's existence cannot simply be demonstrated by speculative reason, theology must ask what kind of knowledge of God is actually possible.

Barth's theology ultimately rejected the attempt to make theology dependent upon autonomous human reason. Yet the Kantian revolution remained part of the intellectual environment in which Barth's theology developed.

A striking later judgment comes from the Kant scholar Heinz Cassirer, who was reportedly astonished by Barth's understanding of Kant:

"Why is it that this Swiss theologian understands Kant far better than any philosopher I have come across?"

That remark is especially interesting because it suggests that Barth did not merely oppose Kant; he understood the force of Kant's philosophical revolution sufficiently well to engage it at a deep level.

Barth's verdict: Human reason cannot manufacture knowledge of God; theology must therefore begin elsewhere than autonomous philosophical speculation.

17. Alfred North Whitehead (1861–1947)

Whitehead's philosophy developed in a very different direction from Kant, but the Kantian question remained important:

How does the structure of experience relate to the structure of reality?

Kant had placed enormous emphasis upon the contribution of the subject to experience.

Whitehead instead developed a philosophy in which experience itself became fundamental to the structure of reality.

The difference is subtle but profound.

Kant:

How does the mind structure the world as experienced?

Whitehead:

What if experience is not merely something occurring inside human minds but is woven into the structure of reality itself?

In that respect, Whitehead can be read as taking one of Kant's deepest questions and moving it into metaphysics.

18. Rudolf Steiner (1861–1925)

Steiner's response to Kant was strongly critical because Steiner believed Kant had imposed an artificial barrier between human cognition and reality.

For Steiner, cognition was capable of penetrating more deeply into reality than Kant's critical philosophy allowed.

His summary of the Kantian position was:

"We know nothing of the thing in itself."

Steiner then characterized the Kantian world as one in which the experienced world is constituted through the forms of sensibility and understanding.

Steiner's own project sought to overcome this separation by developing a conception of cognition capable of reaching reality itself.

Steiner's verdict: Kant mistook the limitations of a particular mode of cognition for the limits of cognition itself.

19. The Larger Pattern

When the responses of these thinkers are placed beside one another, something remarkable appears.

Schopenhauer

Kant discovered the structure of phenomenal experience—but did not go far enough into reality itself.

Hegel

Kant discovered the self-critical activity of reason—but unnecessarily restricted reason's development.

Fichte

Kant discovered the importance of the subject—but the subject is more active than Kant allowed.

Schelling

Kant exposed the limits of reason—but being itself cannot simply be reduced to those limits.

Goethe

Kant analyzed the conditions of experience—but nature must also be encountered directly and concretely.

Jacobi

Kant's thing-in-itself creates a problem: how can something unknowable be invoked as a cause of experience?

Nietzsche

Kant universalized morality without adequately investigating its historical and psychological origins.

Kierkegaard

Kant's rational moral subject is not yet the concrete existing individual.

Russell

Kant's account of a priori knowledge unnecessarily restricts the reach of logic and mathematics.

Strawson

Kant discovered enduring truths about objective experience, but some of his metaphysical conclusions can be discarded.

Heidegger

Kant's critique of knowledge conceals a deeper question about Being and human existence.

Cassirer

Kant's analysis of the conditions of experience can be expanded into a philosophy of symbolic culture.

Barth

Kant demonstrated the limits of autonomous speculative reason, making the question of revelation more rather than less significant.

Steiner

Kant mistook the limits of one mode of cognition for the limits of knowledge itself.

20. The Extraordinary Thing About Kant

Perhaps the most revealing fact about Kant is not that these thinkers agreed with him.

They did not.

It is that they could not get around him.

The great post-Kantian philosophers repeatedly took one of Kant's insights and asked:

What happens if we take this even farther?

Fichte took the subject farther.

Hegel took reason farther.

Schelling took being farther.

Schopenhauer took the thing-in-itself farther.

Nietzsche took the critique of morality farther.

Heidegger took the question of the conditions of experience toward Being.

Strawson separated Kant's durable arguments from his metaphysical framework.

Cassirer expanded the transcendental question into culture.

In that sense, Kant became less a philosophical destination than a continental divide.

One could cross it in many different directions, but one could scarcely pretend it was not there.

21. A Final Mental Anchor

Kant changed the question.

Before Kant, philosophers commonly asked:

What is reality?

Kant forced philosophy to ask:

Before asking what reality is, what must be true about the knower for reality to be experienced and known at all?

And after Kant, an extraordinary new question appeared:

Did Kant discover the actual limits of human reason—or only the limits of the particular conception of reason he had constructed?

That question became the great inheritance of German Idealism, Romanticism, existentialism, phenomenology, and much of modern philosophy.

Kant did not end the Great Conversation.

He changed its grammar.