Immanuel Kant

Roused from his dogmatic slumber by Hume, Kant rejects both opposing paths: dogmatic metaphysics, which claims to know the unconditioned, God, the soul, the world as a totality, loses itself in the antinomies, where reason contradicts itself; yet Humean skepticism, dissolving necessity into habit, is just as untenable. The critical path settles it: there is indeed an apodictic certainty, that of synthetic a priori judgments, but it holds only of appearances, objects as they appear to us under the forms of the subject, not of things in themselves. A necessary and universal certainty, then, but paid for with an impassable limit.

I freely admit that it was the objection of David Hume that, many years ago, first interrupted my dogmatic slumber.Prolegomena, Preface

Critique of Pure Reason, Prefaces and Transcendental Dialectic · Prolegomena to Any Future Metaphysics

The dispute between rationalism and empiricism is insoluble so long as one term is asked to carry everything: experience alone never yields necessity (Hume's objection about causation), reason alone runs idle. Kant's answer is the synthetic a priori judgment: there are a priori forms of sensibility and understanding that structure any possible experience, so that knowledge begins with experience without deriving wholly from it. This is the Copernican turn applied to knowledge, and the reason the axis settles at the centre.

Thoughts without content are empty, intuitions without concepts are blind.Critique of Pure Reason, A51/B75

Critique of Pure Reason, Introduction · Critique of Pure Reason, A51/B75

Dare to know: leaving the minority for which one is oneself responsible requires relying on one's own understanding alone, and wherever a truth can be established, within the field of possible experience, it prevails without rival. But critique bounds that field: beyond it reason no longer knows, and claiming knowledge there would be dogmatism; rational faith does not replace an available truth there, it occupies a place that knowledge structurally cannot fill.

Sapere aude! Have courage to use your own understanding: this is the motto of the Enlightenment.An Answer to the Question: What Is Enlightenment?

What Is Enlightenment? (1784) · Critique of Pure Reason, B preface (1787)

The third antinomy sets a seamless determinism against the demand for a free causality, and both theses seem equally provable. Kant resolves it through the phenomenon / thing-in-itself distinction: determinism governs the human being as phenomenon, yet nothing forbids thinking him a free cause at the noumenal level. The moral law requires it: "you ought" implies "you can", so freedom is a fact of practical reason. Hence the explicit rejection of compatibilism (a wretched subterfuge); but since freedom stays noumenal, never observed in the world, the score stops short of the extreme.

Critique of Pure Reason, Third Antinomy · Critique of Practical Reason

Theoretical reason cannot prove that the soul survives the body, but practical reason postulates it: the moral law commands a perfection that no finite life completes, which requires an indefinite progress, hence the immortality of the soul. An immortality not demonstrated but postulated, a rational belief resting on morality.

Critique of Practical Reason, Dialectic, II

Inclinations are not evil in themselves, but they cannot ground moral worth: an action has value only when done from duty, independently of any inclination. This moral disinterestedness requires that the will make itself autonomous with regard to desire, acting against it where need be; without preaching the extinction of inclinations, Kant keeps a distance from them that leans toward detachment more than toward their eudaimonist sorting.

Groundwork of the Metaphysics of Morals, I-II · Critique of Practical Reason

"What may I hope?" is one of the three cardinal questions of philosophy. The postulates of practical reason, freedom, immortality of the soul and God, ground a rational hope that the highest good, the accord of virtue and happiness, is possible: an avowed principle of hope.

Two things fill the mind with ever new and increasing admiration: the starry heavens above me and the moral law within me.Critique of Practical Reason, Conclusion

Critique of Pure Reason, Canon of Pure Reason · Critique of Practical Reason, Dialectic

Nothing is good without limitation except a good will: morality, not happiness, is the supreme good and the condition of all worth. The complete highest good does include happiness, but only proportioned to virtue and as crowning it, hence a minority eudaimonist weight and the exclusion of hedonism.

Nothing in the world, indeed nothing even beyond the world, can possibly be conceived which could be called good without qualification except a good will.Groundwork of the Metaphysics of Morals, section I

Groundwork of the Metaphysics of Morals, section I · Critique of Practical Reason, Dialectic, II

Nothing is good without qualification except a good will: neither talents nor happiness, which can serve evil. If moral worth lies neither in the object willed nor in the consequences, it can lie only in the form of the maxim, its fitness to hold as a law for all. From this the categorical imperative is derived: act only on a maxim I can will to be universal. This is a deontology that refuses, against utilitarianism, to measure duty by outcome; the Doctrine of Virtue reintroduces the virtues, but as derived from duty, hence a small residual weight on that pole.

Act only according to that maxim whereby you can at the same time will that it should become a universal law.Groundwork of the Metaphysics of Morals, section II

Groundwork of the Metaphysics of Morals, sections I and II · Metaphysics of Morals, Doctrine of Virtue

The moral law holds universally for every rational being, independently of cultures and inclinations: this is the most assertive universalism in the tradition. A slight constructivist weight is warranted by autonomy: the law is not discovered in the world, reason gives it to itself.

Groundwork of the Metaphysics of Morals, section II · Critique of Practical Reason

Against Benjamin Constant, Kant maintains that truthfulness is an unconditional duty, even toward the murderer asking where one's friend is hiding: lying would destroy the foundation of all right. This is the textbook case of truth-telling rigorism.

On a Supposed Right to Lie from Philanthropy

A maxim has moral worth only if I can will it to become a universal law holding for every rational being, with no exception in my favour or for those close to me. The categorical imperative excludes by construction any privilege granted to oneself or one's own, hence an almost pure impartialism.

Groundwork of the Metaphysics of Morals, section II

Duty imposes itself as a strict law that reason gives to itself, and Kant draws from it a famous rigorism: the prohibition of lying admits no exception, even to save a life. The slightest yielding to circumstances would ruin the unconditionality of the moral law, placing Kant firmly on the legalist side.

On a Supposed Right to Lie from Philanthropy · Groundwork of the Metaphysics of Morals, section II

Right is derived a priori from reason, not from utility nor from positive law alone: every human being possesses, by virtue of their humanity, an innate right to freedom, grounded in the dignity of the person as an end in itself. A rational version of natural rights.

The Metaphysics of Morals, Doctrine of Right

Kant defends cosmopolitan right and the idea of a federation of free states as the horizon of history: every human being has a right of universal hospitality as a citizen of the earth. The nation state remains a necessary mediation, which qualifies the score.

Perpetual Peace · Idea for a Universal History with a Cosmopolitan Purpose

Punishment is demanded by justice itself, as retribution proportionate to the crime (juridical law of retaliation), never as a mere means of social utility: punishing someone to deter others would treat him as a means. This is classical retributivism.

Metaphysics of Morals, Doctrine of Right, §49 E

Kant reads history as the unfolding of a plan of nature: through the "unsocial sociability" of human beings, the species advances toward a perfect civil constitution and a peaceful federation of peoples. This is a directional history, conceived as a regulative idea rather than as sheer contingency.

Idea for a Universal History with a Cosmopolitan Purpose

Enlightenment is the human being's emergence from his self-incurred immaturity. Kant makes the free public use of reason the engine of a gradual progress of humanity, placing him clearly on the progressist side.

Sapere aude! Have courage to use your own understanding: this is the motto of the Enlightenment.An Answer to the Question: What Is Enlightenment?

An Answer to the Question: What Is Enlightenment?

The civil condition rests on an original contract, not as a historical fact but as an idea of reason: the criterion of a just law is that it could have received the assent of the whole people. The legitimacy of power is grounded on this rational agreement, an avowed contractualism.

On the Common Saying: That May Be Correct in Theory, but It Is of No Use in Practice · Metaphysics of Morals, Doctrine of Right

Kant asserts a duty to obey the established power and denies any right of resistance or revolution, even against an unjust sovereign, since overturning the constitution would ruin the rule of law itself. The citizen retains the freedom to criticise publicly in writing, but must obey.

Argue as much as you will and about what you will, but obey!An Answer to the Question: What Is Enlightenment?

Metaphysics of Morals, Doctrine of Right, §49 · An Answer to the Question: What Is Enlightenment?

Since all knowledge is bounded to phenomena, God, who is not one, escapes proof: Kant dismantles the proofs of God's existence one by one (ontological, cosmological, physico-theological), the first failing in its leap from concept to existence. Yet what is barred to knowledge is required by morality: without God and immortality, the accord of virtue and happiness (the highest good) would stay unthinkable. God thus returns as a postulate of practical reason, an object of rational faith and not of knowledge, which warrants a moderate rather than an assertive theism.

Critique of Pure Reason, "Transcendental Ideal" · Critique of Practical Reason, Dialectic

The judgment of taste is subjective (it rests on no concept of the object) yet legitimately claims universality. This is exactly the axis's named median position, subjective universality.

The beautiful is that which pleases universally without a concept.Critique of the Power of Judgment, §9

Critique of the Power of Judgment, §6-§9

If the mind conformed to objects, we could never know anything of them a priori; reverse the hypothesis, as Copernicus set the observer at the centre, and let objects conform to our cognition. Then space, time and the categories are not features of things but the forms of the subject under which alone an object can appear to us. The consequence is transcendental idealism: we know only phenomena, never the thing in itself. This boundary saves science (its laws hold necessarily for every phenomenon) without collapsing into Berkeley's idealism, since the thing in itself remains; the phenomenon / noumenon dualism thus kept rules out the fully idealist pole.

Critique of Pure Reason, Transcendental Aesthetic · Prolegomena to Any Future Metaphysics, §13

Causality is an a priori category of the understanding that structures every phenomenon by mechanical law: known nature is a deterministic chain of cause and effect. The third Critique adds purposiveness, but Kant declares it merely regulative, a principle for judging living things rather than a mechanism of the world, hence a minority finalist weight.

Critique of Pure Reason, Second Analogy of Experience · Critique of the Power of Judgment, §§61-68

Theoretical reason can neither prove nor refute God, but practical reason postulates a rational faith attuned to morality. Faith and knowledge thus occupy distinct domains while harmonising under the primacy of the practical, with a fideist nuance since faith remains a need of reason rather than a matter of proof.

I had to deny knowledge in order to make room for faith.Critique of Pure Reason, Preface to the Second Edition (B XXX)

Critique of Pure Reason, Preface to the Second Edition (B XXX) · Religion within the Bounds of Bare Reason