Immanuel Kant

Last updated: 2025-12-10

Personal life

The life of Immanuel Kant (1724–1804) was one of the most regular, methodical, and apparently "boring" in the history of philosophy, but precisely that extreme discipline allowed him to produce one of the most revolutionary works of human thought.

Main stages of his life

Birth and youth (1724–1755)
He was born on April 22, 1724 in Königsberg, East Prussia (today Kaliningrad, Russia), into a modest family of Pietist artisans (a very strict and devout Protestant current). He was the fourth of nine children, of whom only five reached adulthood.
His mother, Anna Regina, had a decisive influence: she was a cultivated woman for her station and instilled in him the love of learning and rigorous morality. Kant always spoke of her with admiration.
He studied at the Collegium Fridericianum (Pietist school) and then at the University of Königsberg (1740–1746), where he took an interest in philosophy, physics, and mathematics (he was a pupil of the Wolffian Martin Knutzen).
Private tutor stage and "precariousness" (1746–1755)
After his father’s death, he had to temporarily leave the university to work as a private tutor (Hofmeister) in noble families around Königsberg. During these years he traveled a little through East Prussia, the farthest he ever went in his entire life (he never left the province).
Return to the university and academic career (1755–1797)
In 1755 he obtained his doctorate and began teaching as a Privatdozent (unsalaried professor who lived on what the students paid).
He was an extremely popular professor: he taught logic, metaphysics, ethics, physical geography, anthropology, pedagogy, natural law, and even military fortifications and pyrotechnics. Sometimes he had up to 100 students in his courses.
In 1770, at age 46, he finally obtained the chair of Logic and Metaphysics (the great goal of his academic life). That same year he published his inaugural dissertation in Latin: De mundi sensibilis atque intelligibilis forma et principiis (the seed of the future Critique of Pure Reason).
The "silent decade" (1770–1781)
After obtaining the chair, Kant entered a phase of deep reflection and published almost nothing important. He was gestating his critical system. His friends worried because it seemed he "had dried up."
The critical stage: the great works (1781–1790)
– 1781: Critique of Pure Reason (1st edition) → revolutionized philosophy.
– 1785: Groundwork of the Metaphysics of Morals.
– 1787: Critique of Pure Reason (2nd edition, much clearer).
– 1788: Critique of Practical Reason.
– 1790: Critique of Judgment.
With these three critiques he built his complete philosophical system.
Final years and decline (1797–1804)
In 1797, at age 73, he stopped teaching due to health problems.
From 1801 his memory began to fail seriously (probably dementia or vascular deterioration). His friends (including his doctor) had to care for him.
He died on February 12, 1804 at 11 in the morning. His last intelligible words were: „Es ist gut“ ("It is good").
His funeral was a mass event in Königsberg: thousands of people accompanied him, and the bells of all the churches rang for hours.

Curiosities about his character and daily routine

He never married nor had a known partner (it is said that on two occasions he was about to propose marriage to a woman, but he thought about it so long that when he decided, she had already married).
His life was of almost pathological regularity: the neighbors of Königsberg set their clocks by him when they saw him go out for his walk at exactly 3:30 p.m. (he was late only once in his life: the day he was reading Rousseau’s Émile and lost track of time).
He always walked the same path (the famous "Philosopher’s Walk"), alone, at a constant pace, without an umbrella even if it rained (he said that breathing moist air was healthy).
He was a hypochondriac; he obsessively controlled his diet, breathing, and sleep.
He was very sociable: he dined every day with friends (never fewer than 3 nor more than 9 guests, according to him the ideal number); he loved conversation and was an exquisite host.
He measured 1.57 m and in his final years weighed barely 40–45 kg.
He had a portrait of Rousseau in his study (the only decoration he had)

In summary: Kant lived 80 years practically without leaving Königsberg, with an almost monastic routine, but in that small Baltic city and with that iron discipline he forever changed the way we understand knowledge, morality, and aesthetics. As he himself said: «Two things fill the mind with admiration and respect: the starry sky above me and the moral law within me». And he discovered both without barely moving from his desk.

What inspired Kant for his ideas?

If Hobbes was the architect of order and Rousseau the defender of goodness, Immanuel Kant was the "Great Synthesizer." Kant not only drew inspiration from others; he took the two greatest and most opposed currents of his time —Rationalism and Empiricism— and united them into something completely new.

Here are the authors and currents that "awakened" Kant’s mind:

1. David Hume: The intellectual "alarm clock"

Kant was originally a very traditional philosopher until he read the Scot David Hume.

The influence: Kant confessed that Hume awoke him from his "dogmatic slumber". Hume argued that we cannot be sure of cause and effect (we only see that something happens after something else, but not the "connection").
The result: Kant became obsessed with answering Hume. This led him to write the Critique of Pure Reason, where he explains that the human being is born with mental "filters" (such as time and space) to organize reality.

2. Jean-Jacques Rousseau: The "Newton of morality"

If Hume influenced how Kant thought about science, Rousseau influenced how he thought about people.

The influence: Kant had a portrait of Rousseau in his study (the only decoration he had). From him he learned that human dignity is the supreme value.
The change: Before Rousseau, Kant believed that intelligence was the most important thing; after reading him, he understood that the most valuable thing is moral freedom and justice. Without Rousseau, Kant’s famous "Categorical Imperative" would not exist.

3. Isaac Newton: The model of truth

Kant lived in the era of Newtonian physics and admired it deeply.

The goal: Kant wanted philosophy to be as solid and exact as Newton’s physics.
The application: A large part of his work consisted in demonstrating why Newton’s laws were true and necessary for our way of understanding the physical world.

4. Gottfried Leibniz and Christian Wolff: The schoolmasters

Kant was educated in the German tradition of these two philosophers (Rationalism).

What he took: From them he learned the importance of system and logic. His books are written in an extremely structured and difficult way because he wanted every piece to fit perfectly with the previous one, like a perfect machine.
What he rejected: He criticized them for being "dogmatic," that is, for believing that reason could explain God or the soul without need of empirical proofs.

5. Pietism (Family influence)

More than an author, it was his religious education. Pietism emphasized discipline, duty, and the inner life.

This rigidity is noticeable in his ethics: for Kant, what matters is not whether an action makes you happy, but whether it is your duty to do it.

Kant said that while Newton discovered the order of the physical universe, Rousseau discovered the order of the moral universe.

What is Immanuel Kant’s ethical thought?

Immanuel Kant’s (1724–1804) ethical thought centers on deontology (deon = "duty"), an ethical theory based on duty and reason, not on consequences.

His main idea is the categorical imperative, which establishes that we must act according to rules that can be universalized (in every time and place) without contradiction and that respect persons as ends in themselves, not as means.

Categorical imperative:
- "Act only according to that maxim which you can at the same time will that it become a universal law". Your actions must be coherent with principles that everyone could follow. EX: Do not lie, do not kill, under any circumstance or excuse.
  - Ex: A person tells a lie to get out of a tight spot. Kant would ask for a thought experiment: What would happen if everyone, by natural law, had to lie whenever they were in a tight spot?
Autonomy and dignity:
- "Act in such a way that you treat humanity, whether in your own person or in the person of any other, always as an end and never merely as a means".
- Humanity is in itself the end of things, not a tool for achieving ends. This is the basis of modern Human Rights. For Kant, persons have "dignity," not a "price"; they are not objects for reaching an end.
Reason as a guide:
- Ethics is based on pure reason, not on emotions, not on desires, not on preferences or tastes, not on results; rather, reason must analyze all of these aspects.
- Reason is the source of ethics. Every person, by being rational, can discover what is good and act according to laws that they give themselves (autonomy).
- The Categorical Imperative is possibly the most famous tool in the history of ethics. Kant wanted to find a "moral law" that did not depend on religion or on feelings, but purely on reason.
Duty above all:
- What matters is not the result, but acting from duty, because we recognize that something is the right thing to do.
- For Kant, consequences can be unpredictable; the only thing we control is our intention.

Kant emphasizes universality, rationality, and respect for humanity as the basis of ethics.

Criticisms of Kant’s ethics

Kant is one of those who receive the most criticism; I will name only some:

Too abstract: It is criticized for being too abstract and formal. The categorical imperative ("act according to the maxim that you can will as a universal law") does not offer concrete guidance for specific situations, which can make its practical application difficult.
Disconnection from emotions: Kant prioritizes reason over emotions (which for him have no importance)
Disconnection from consequences: Kant does not take into account the results of actions, only the intention.
Too rigid: Kant requires that morality be absolutely rational and universal, without exceptions. This can lead to absurd or inhumane conclusions (Example: not lying to save someone’s life). This rigidity does not consider the complexity of human circumstances or conflicts between duties.

What did Kant think about the State?

Immanuel Kant’s thought on the State is deeply linked to his moral and legal philosophy. In essence, Kant conceives the State not as a tool for achieving happiness or well-being, but as the guarantee of right and the only rational means to secure the liberty of all individuals.

Here is a concise summary of his main ideas about the State:

The State as Rational and Legal Necessity

The State of Nature and Reason: Kant follows the contractualist tradition (like Hobbes and Locke), but argues that leaving the State of Nature is not only desirable, but a rational duty. In the natural state, there is no authority that enforces rights, so property and liberty are insecure. Reason demands the establishment of a public order. > It is a practical categorical imperative to leave the state of nature and form a Civil State.
The Rule of Law (Rechtsstaat): The principal function of the State is to guarantee Right and the coexistence of liberties. The State must be a state under the rule of law, where the government itself is subject to just laws.
- Right: It is the limitation of each person’s liberty to the condition of its accordance with the liberty of all, insofar as this is possible according to a universal law.
The Social Contract (Hypothetical): Kant does not see the social contract as a real historical event, but as an Idea of Reason or a regulative principle. The State must legislate as if its laws had emanated from the united will of the entire people. This secures the legitimacy of the laws.

A Priori Principles of the Civil State

The State, as a pure form of Right, is founded on three rational and non-negotiable principles:

Liberty: Every member of society is free as a human being. Liberty is the capacity to pursue one’s own happiness as one wishes, so long as one does not invade the liberty of others (negative liberty). The State must not prescribe happiness.
Equality: Every member of society is equal to the others as a subject. All are equally subject to the law and to public coercion, except the head of State (the legislator).
Autonomy (or Independence): Every member of society is independent as a citizen and therefore has the right to participate as co-legislator (although Kant restricted the right to vote to "active citizens" with property or economic self-sufficiency).

The Form of Government

Kant favored the Republic as the ideal form of government. A republic is characterized by:

Separation of Powers: Division among the legislative power (supreme), executive, and judicial.
Representation: Citizens (active ones) elect their representatives.
Avoiding Despotism: A form of government that does not separate the executive power from the legislative becomes despotism, for the ruler who makes the law also executes it according to his particular will.

Kant was a fundamental defender of political libertarianism and of the rule of law, seeing the State as the rationally necessary institution for establishing a legal order that guarantees the external liberty of all under a universal law.

Criticisms of Kant’s ideas

The ideas of Immanuel Kant (both in ethics and in political philosophy and the State) have been the object of very intense criticism from his time to today. Here is an ordered summary of the main criticisms, classified by theme:

1. Criticisms of Kantian ethics (categorical imperative)

Main critic	Essential criticism
Hegel	Kantian morality is “abstract” and “empty.” The categorical imperative is mere formalism that does not say what to do concretely; it only gives a test of universality that can be manipulated.
Schiller	He joked that, according to Kant, only someone who helps a friend reluctantly and from pure duty, never from affection, would be moral.
Schopenhauer	He called Kant’s ethics “disguised theology” and accused it of hypocrisy: in reality Kant surreptitiously introduces Christian commandments (do not lie, do not commit suicide) dressed up as pure reason.
Utilitarians (Bentham, Mill)	The ethics of duty ignores consequences. It forbids lying even to save a life (classic example of the murderer at the door), which is inhumane and rigid.
Virtue ethics (Anscombe, MacIntyre)	Kant eliminates feelings, inclinations, and character; he turns morality into cold obedience to a self-imposed law.
Feminists (Carol Gilligan, etc.)	Kantian ethics is “masculine”: it prioritizes abstract and universal justice over care, relationships, and context.

2. Criticisms of political philosophy and the concept of the State

Main critic	Essential criticism
Hegel	Kant remains at the “ought” (Sollen). The Kantian State is a regulative idea, but Hegel affirms that the real Prussian State is already the realization of concrete freedom, not a future ideal.
Marx and Marxists	Kant is the typical philosopher of the bourgeoisie: he defends private property as a condition of active citizenship and excludes workers, women, and the poor from the right to vote. His “perpetual peace” is a liberal utopia that masks imperialism.
Carl Schmitt	Kant is naïve in believing that law and morality can dominate politics. Real politics is based on the friend-enemy distinction; the Kantian idea of a world federation ignores sovereignty and inevitable conflict.
Feminists and postcolonials	Kant explicitly excludes women, servants, and “apprentices” from active citizenship. Moreover, his texts on races and non-European peoples contain very harsh racist and Eurocentric statements.
Revolutionary liberals (Paine, young Fichte)	Kant rejects any right of resistance or revolution. That makes him a defender of the status quo, even in the face of tyrants.

3. Specific criticisms of the cosmopolitan project and “perpetual peace”

Main critic	Essential criticism
Realists (Morgenthau, Kissinger)	The idea that democratic republics do not make war on each other (“Kantian democratic peace”) is empirically doubtful and politically naïve.
Postcolonials (Said, Spivak, etc.)	Kantian “cosmopolitanism” is Eurocentric: the universal hospitality he proposes applies only among “civilized States” (European ones); colonized peoples are denied even the right to sovereignty.
19th-century nationalists	Kant dissolves the nation and sovereignty into a world federation; that goes against the national spirit and the will to power of peoples.

4. General criticisms of his style and method

Fichte, Schelling, Hegel: They accused Kant of remaining in irreconcilable dualisms (phenomenon/noumenon, sensibility/understanding, theory/practice) that later German idealism tried to overcome.
Nietzsche: Kant is the maximum representative of slave morality and of “rational asceticism”: he turns duty into a new idol.

In summary

Although Kant is one of the most influential thinkers of modernity, his critics agree in pointing out:

Rigidity and excessive formalism in ethics.
Political conservatism (rejection of revolution and resistance).
Eurocentrism, racism, and gender exclusion in his anthropological and political texts.
Enlightened naïveté in believing that pure reason can by itself found right and world peace.

Despite everything, many of his ideas (human dignity, universal rights, constitutionalism, the cosmopolitan project) remain the basis of the current liberal order, so the criticisms have not managed to displace his enormous legacy.

What criticisms did his personal life receive?

It is important to note that, unlike the criticisms of his philosophy, the criticisms or comments on the personal life of Immanuel Kant (1724–1804) do not center on grave moral scandals or ethical controversies. Instead, they focus on the peculiarities of his lifestyle, which was marked by rigorous discipline, routine, and solitude.

Here is a summary of the main comments and criticisms of his personal life:

1. Criticisms of his Extremely Methodical Lifestyle

The most common criticism is that Kant’s life was too rigid and enslaved to routine, almost an incarnation of his own duty-based ethics:

Rigid Routine: Kant was famous for his immutable schedule. He got up exactly at 5:00 a.m., drank tea and smoked a pipe, gave his classes, wrote, and, most famously, went out for a walk at 3:30 p.m. His routine was so predictable that the inhabitants of Königsberg (his native city, where he never traveled more than a hundred miles) supposedly set their clocks by his walk. > Criticism: This methodical life was seen by some as an "unlived" life, excessively centered on reason and theory, and lacking the spontaneity and richness of human experience.
Obsession with Health: Kant was deeply concerned with his health and longevity, despite a weak constitution. He wrote essays on how the will can control diseases. > Criticism: His life as a self-imposed ascetic was interpreted as a phobia of illness or an exaggeration of discipline, rather than a simple preference.

Kant never married and led a fairly solitary life, which generated comments about his understanding of full human experience:

Lack of Life Experience: He is criticized that, by not having a deep family or affective life, and by never traveling, his philosophy could be too abstract or lack a foundation in the complexity of real human relationships (love, sacrifice, passion, etc.) that so much influence morality. > Famous Comment: The German philosopher Arthur Schopenhauer (who was a harsh critic of Kant) joked that Kant only knew human experience through reading.
Relationships with Women: Kant maintained friendships with women, but never completed marriage, despite having considered it twice. It has been speculated that his extreme dedication to work or his phlegmatic nature prevented him from establishing lasting intimate bonds. > Criticism: Some see it as a manifestation of the same Cartesian separation between reason and emotion that permeates his ethics.

The Alleged "Rational Egoism"

Some commentators suggest that Kant’s life, devoted entirely to self-preservation, health, discipline, and work, can be seen ironically as a form of rational egoism or self-adoration of one’s own reason, even though his ethics condemned egoism.

Little Real Social Commitment: Although he was hospitable and liked to have guests for dinner (where talking about philosophy was forbidden so that conversation would be "stimulating"), his social life was strictly programmed and controlled, which limited his true engagement with the community beyond his academic responsibilities.

The "criticisms" of Kant’s personal life are rather observations about his eccentricity and rigor, which his critics often use to argue that his philosophy lacks an understanding of the richness and passions of human existence.

What is Kant’s legacy?

Immanuel Kant is, alongside Plato and Aristotle, one of the three most influential philosophers in Western history. His impact extends to almost every area of modern thought and practice.

The legacy of Immanuel Kant is monumental, covering philosophy, ethics, politics, and aesthetics. He definitively transformed the way the West thinks about morality, knowledge, and the nature of reality.

Here is a summary of his most enduring legacy, divided by areas:

The Epistemological and Metaphysical Legacy (The "Copernican Revolution")

Kant resolved the conflict between rationalism (which emphasizes a priori reason) and empiricism (which emphasizes a posteriori experience) with his masterwork, the Critique of Pure Reason.

The Copernican Revolution: His great paradigm shift was to suggest that, instead of our knowledge conforming to objects (as traditionally thought), objects must conform to the a priori structure of our mind. That is, we cannot know the world as it is in itself, but only as it appears to us, filtered through the structures of our consciousness.
Phenomenon and Noumenon: By distinguishing the phenomenon (the world as we experience it) from the noumenon or "Thing in Itself" (unknowable reality), Kant established the limits of human reason. He demonstrated that traditional metaphysics (trying to know God, the soul, or the universe) is doomed to failure because it transcends possible experience.
Foundation of Science: By establishing that categories such as causality are not only empirical habits (as Hume said), but innate structures that the mind imposes on experience, Kant provided a solid basis for the necessity and universality of scientific laws (such as Newton’s physics).

The Ethical Legacy (Moral Rationality)

Kantian ethics, contained mainly in the Groundwork of the Metaphysics of Morals and the Critique of Practical Reason, is the most influential model of deontological ethics (based on duty).

The Categorical Imperative: This principle is his most famous contribution. By requiring that the maxim of an action be universalizable without contradiction, Kant offered a rational procedure for determining morality, instead of depending on religion, emotion, or consequences.
Human Dignity and Rights: His formulation of Humanity ("act in such a way that you use humanity... always at the same time as an end, and never merely as a means")

[Image of scales of justice] , is the fundamental philosophical basis for the modern concept of Human Dignity and universal Human Rights. He postulated that persons have an intrinsic and absolute value, which is central to contemporary law. * Autonomy of the Will: Kant elevated freedom by postulating that a moral being is an autonomous being, who gives the moral law to himself through his own reason. To be moral is to be free.

The Political and Legal Legacy

Kant’s ideas on the State laid the foundations of modern libertarianism and international law.

The Rule of Law (Rechtsstaat): He defined the State as an institution whose only legitimate function is to secure the coexistence of the liberty of all under a universal law. This is the modern conception of the liberal and constitutional State.
Perpetual Peace: His essay Toward Perpetual Peace (1795) is considered a foundational text of International Law and of theories of liberal International Relations. He proposed the creation of a "Federation of Free States" (a kind of League or United Nations avant la lettre) and advocated the adoption of republican constitutions as requirements for lasting peace.

The Aesthetic and Teleological Legacy

In the Critique of Judgment, Kant addressed aesthetics and purpose in nature.

The Beautiful and the Sublime: He established key distinctions in aesthetics, separating the judgment of the beautiful (which provides a "disinterested pleasure") from the sublime (which evokes awe and even terror, revealing the immensity of nature and the moral superiority of the human being).
Bridge Function: This critique served as a bridge between the deterministic laws of nature (established in the Critique of Pure Reason) and the freedom of morality (treated in the Critique of Practical Reason), deeply influencing the Romantic movement.

Kant founded the intellectual and political world in which we still live: the idea that human reason can and must give itself its own laws (autonomy), that every person has absolute dignity, and that history must move toward a global legal order based on liberty and peace. That is why it is said that “we cannot think after Kant as one thought before him.” His legacy is not only academic: it is written in constitutions, in international courts, and in modern moral consciousness.

Most important phrases

"Act only according to a maxim such that you can at the same time will that it become a universal law."
- (The first formulation of the Categorical Imperative, the golden rule of his ethics.)
"Act in such a way that you use humanity, whether in your own person or in the person of any other, always at the same time as an end, and never merely as a means."
- (The formulation of Humanity, which establishes the Dignity and intrinsic value of each person.)
"A good will is not good because of what it effects or accomplishes, nor because of its fitness to attain some proposed end; it is good only through its willing, that is, it is good in itself."
- (Defines Good Will as the only thing absolutely good, independent of consequences.)
"Two things fill the mind with ever new and increasing admiration and reverence, the more often and more steadily we reflect on them: the starry heavens above me and the moral law within me."
- (One of the most poetic and famous phrases, which appears at the end of the Critique of Practical Reason, summarizing the two great areas of his philosophy: the natural world and morality.)
"Right is the limitation of each person’s liberty to the condition of its accordance with the liberty of all, insofar as this is possible according to a universal law."
- (His formal definition of Right.)
"Peace is not the natural state of men."
- (Affirmation that peace must be established through laws and treaties; it is not something that occurs spontaneously, according to his essay Toward Perpetual Peace.)
"The beautiful is that which pleases universally without a concept."
- (His definition of the Aesthetic Judgment or of the beautiful, which is subjective but claims universal validity.)

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Last updated: 2025-12-12

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