Immanuel Kant

Justice

Justice is the universal law of freedom: the condition in which each person's freedom can coexist with all others'.

Good and Evil

The only unconditionally good thing is a good will: acting from duty, not inclination.

Virtue and Vice

Virtue is the strength of the moral will: acting from duty against inclination.

Happiness

Morality is not the doctrine of how we may make ourselves happy, but of how we may become worthy of happiness.

Courage

Courage has moral worth only when it serves duty; bravery without a good will is merely dangerous.

Desire

Desire belongs to our animal nature; moral action requires acting from duty against the pull of inclination.

Punishment

Punishment is a categorical imperative: the criminal must receive what he deserves, regardless of any benefit to society, because to punish for utility is to use a person as a mere means.

Duty

Duty is obedience to the moral law within; the categorical imperative makes duty coextensive with all morality.

Emotion

The passions must not determine the will; only respect for the moral law is a morally worthy motive.

Pleasure and Pain

Pleasure cannot ground the moral law; duty opposes inclination, and a good will acts from respect for law, not from desire for satisfaction.

Temperance

Self-mastery is a duty, not a pleasure: the moral worth of temperance lies in willing it from principle rather than inclination.

Liberty

Freedom is autonomy: the self-legislation of the rational will.

Government

Legitimate government is republican: law-governed, representative, with separated powers.

Law

Public right is the universal law of freedom: conditions under which external wills can coexist.

War and Peace

Perpetual peace is a moral imperative. It requires a federation of free states.

Citizen

Citizenship is grounded in three juridical attributes: constitutional freedom, civil equality, and political independence — though the last requires economic self-sufficiency that not all yet possess.

Constitution

The only legitimate constitution is the republic, defined not by who rules but by whether lawmaking is separated from the administration of law.

God

We cannot know God through theoretical reason. God is a postulate of the moral life.

Soul

We cannot know the soul as substance. But its immortality is a postulate of practical reason.

Being

Being is not a real predicate, and the thing-in-itself lies forever beyond our knowledge.

Cause

Causality is not derived from experience but is a condition under which experience is possible.

Time

Time is not a thing out there but the a priori form of inner sense: the form under which we experience anything at all.

Religion

God's existence is a postulate of practical reason; true religion is moral religion, and everything beyond duty is superstition.

Immortality

Speculative reason cannot prove the soul's immortality, but practical reason must postulate it as a condition of moral perfection.

Theology

Speculative theology is impossible: reason cannot prove God, but morality demands that we postulate God's existence.

Metaphysics

Metaphysics as a science of supersensible reality is impossible; but a critique of reason can determine what we can and cannot know a priori.

Change

Change is a succession of determinations of a substance that itself persists, a rule the mind imposes to make experience possible.

Form

Form is not in things but in the knower: space and time are forms of intuition, and the categories are forms of understanding.

Matter

Matter is not a thing in itself but the movable in space: an appearance structured by the forms of sensibility and the laws of the understanding.

Necessity and Contingency

Necessity belongs to the forms of experience, not to things in themselves, and the existence of a necessary being cannot be proved.

One and Many

The manifold of sense becomes one world only through the transcendental unity of apperception.

Space

Space is the a priori form of outer intuition; we impose spatial order on experience, not extract it from things.

World

The world as we know it is structured by the mind's own categories; whether the universe is finite or infinite, created or eternal, reason cannot determine.

Opposition

Reason, left unchecked, generates antinomies: pairs of opposed demonstrations on transcendent questions that expose the limits of metaphysics.

Relation

The categories of relation, substance and accident, cause and effect, community of interaction, are forms the understanding imposes on experience, making objective knowledge possible.

Same and Other

The 'I think' must accompany all my representations, yet this unity of apperception is a formal condition of experience, not a substance.

Quality

Quality enters experience through the Anticipations of Perception: every sensation has an intensive magnitude, a degree, that belongs to the form of experience rather than to things in themselves.

Quantity

All intuitions are extensive magnitudes: space and time, as forms of sensibility, make quantity possible, and mathematics is synthetic a priori knowledge.

Angel

Pure intelligences lie beyond possible experience: we can think them without contradiction, but we cannot know that they exist.

Eternity

Whether the world is eternal cannot be decided theoretically, but the moral law demands an endless duration for the soul's progress.

Infinity

Whether the world is finite or infinite cannot be decided by reason; the antinomies show both answers collapse when applied beyond experience.

Truth

Truth is the agreement of knowledge with its object, but objects are constituted by the mind's categories.

Knowledge

The mind contributes structure to experience. We know appearances, not things in themselves.

Mind

Mind is the spontaneous activity that unites experience; its 'I think' must accompany all my representations.

Experience

All knowledge begins with experience, but it does not all arise from experience; the mind contributes the forms that make experience possible.

Will

The autonomous will legislates the moral law to itself; the good will is the only thing good without qualification.

Language

The categories of thought structure experience independently of language, but language remains the necessary medium of communicable knowledge.

Memory and Imagination

Imagination is the power of synthesis that unifies the manifold of intuition; it makes experience possible.

Rhetoric

Oratory as the art of deceiving by beautiful illusion is unworthy of respect; only honest persuasion consistent with moral autonomy is admissible.

Opinion

Opinion, belief, and knowledge are three distinct modes of holding something true, distinguished by the subjective and objective sufficiency of their grounds.

Idea

Ideas of reason are not derived from experience but are necessary concepts that regulate thought beyond what the senses can verify.

Judgment

Judgment subsumes particulars under universals; its synthetic a priori forms make experience itself possible.

Sense

Sensibility provides the raw matter of experience through the forms of space and time, which the mind contributes a priori.

Sign and Symbol

Symbols present concepts indirectly through analogy; aesthetic ideas in art symbolize what no concept can fully express.

Hypothesis

Hypotheses in philosophy are not proofs but regulative ideas that orient inquiry without themselves being objects of knowledge.

Mathematics

Mathematical judgments are synthetic a priori: they extend knowledge beyond concepts, yet hold with universal necessity.

Dialectic

Transcendental dialectic exposes the illusions of reason when it tries to know what lies beyond all possible experience.

Principle

Synthetic a priori principles are not derived from experience but are the conditions that make experience possible.

Reasoning

Reason seeks the unconditioned ground of every conditioned judgment; this drive is both necessary and prone to illusion.

Logic

General logic abstracts from all content of thought and treats only its form; transcendental logic investigates the a priori conditions under which objects first become thinkable.

Induction

The principle of universal causation is not derived from experience but is a condition of the possibility of experience: this synthetic a priori truth answers Hume.

Definition

Strict definition is possible only in mathematics; in philosophy, concepts are given before definitions and must be analyzed rather than constructed.

Universal and Particular

The categories of the pure understanding are universal and necessary concepts that the mind brings to experience; without them, no particular could be recognized as an instance of any kind.

Science

Science is synthetic a priori cognition: it achieves necessity and universality because the understanding prescribes its forms to nature, not because it reads them off from experience.

Education

Education forms autonomous rational agents, disciplining nature to make room for freedom.

Nature

Nature is the realm of appearances governed by law: its order contributed by the mind's own categories.

Wisdom

Wisdom requires knowing the limits of reason and subordinating knowledge to the demands of moral duty.

Prudence

Prudence is legitimate in its own domain but has nothing to do with morality — the confusion of the two is the fundamental error of empiricist ethics.

Philosophy

Critical philosophy asks not what we can know about objects but what conditions make knowledge possible in the first place.

Man

Man is a moral being, distinguished by his capacity to act from duty and to treat humanity as an end in itself.

Beauty

The beautiful is what pleases universally, without concept, through the free play of imagination and understanding.

Art

Fine art is the production of genius: nature giving the rule to art through an inexplicable gift.

Poetry

Poetry is the highest of the fine arts; it conducts a free play of imagination as if it were a serious business of understanding.

Astronomy

The starry heavens above fill the mind with awe; reason can determine the conditions of possible experience but not the ultimate structure of the cosmos.

Evolution

We must judge organisms as if they were designed for purposes, but this teleological judgment is a regulative principle of inquiry, not a constitutive claim about nature.

Mechanics

The laws of mechanics are possible because the mind imposes the categories of substance, causality, and reciprocity on all experience; Newtonian physics presupposes transcendental conditions.

Physics

The laws of physics are possible because the understanding prescribes the conditions under which any experience is possible at all; nature's lawfulness is grounded in the mind.