Aristotle

Justice

Justice is giving each person their due: distributing goods by merit, correcting wrongs by equality.

Good and Evil

The good for humans is eudaimonia: flourishing through virtuous activity over a complete life.

Virtue and Vice

Virtue is a stable disposition to act well: the mean between excess and deficiency.

Happiness

Happiness is activity of the soul in accordance with virtue, over a complete life.

Love

Friendship is one soul in two bodies: the virtuous love each other for the good they share.

Courage

Courage is the mean between cowardice and rashness, exercised by the person who fears the right things for the right reasons.

Desire

Desire is natural appetite directed by reason toward the good; virtue is the habit of desiring rightly.

Punishment

We punish because pain teaches what argument cannot: the person who has not learned virtue by habit may yet learn it by correction.

Duty

Duty arises from justice alone among the virtues, since justice alone concerns another's good.

Emotion

Emotions are judgments about good and evil accompanied by pleasure or pain; the virtuous person feels them at the right time, toward the right objects.

Pleasure and Pain

Pleasure completes activity as bloom completes youth; there are good and bad pleasures, and temperance is the virtue that moderates bodily ones.

Honor

Honor is the proper reward of virtue — but the magnanimous person is not dependent on it.

Habit

We become virtuous by doing virtuous acts: character is built through repeated action, not through understanding alone.

Temperance

The temperate person takes pleasure in the right things in the right measure — and feels no pull toward excess.

Custom and Convention

Natural justice is real but not rigid; it must be completed by the conventions of particular communities.

Liberty

Liberty is self-government: ruling and being ruled in turn among equals.

Government

Government is legitimate when it rules for the common good, not the rulers' private advantage.

Law

The rule of law is better than the rule of any individual, even the wisest ruler.

War and Peace

War is a means, never an end. It exists for the sake of peace.

Democracy

Democracy is rule of the many in their own interest: deviant in principle, workable in practice when mixed.

State

The state is a natural community that exists for the sake of the good life, not merely for survival.

Wealth

Natural wealth-getting serves the household; money-making for its own sake is limitless and contrary to nature.

Revolution

Revolutions arise from inequality and the desire for equality; constitutional moderation is the best prevention.

Tyranny

Tyranny is monarchy that serves the ruler's advantage alone, governing unwilling subjects against their interest.

Family

The family is the first and most natural community — the foundation from which village, city, and political life grow.

Citizen

Citizenship is defined by active participation in government: the citizen is one who rules and is ruled in turn.

Labor

Labor is necessary but servile: those whose lives are consumed by work lack the leisure for virtue, political participation, and the life well lived.

Slavery

Some men are slaves by nature, fitted by their constitution to serve under the direction of a master.

Constitution

The constitution is the arrangement of offices that defines a regime; the best regime mixes oligarchic and democratic elements.

Monarchy

Kingship is the best regime in principle, but it presupposes a man of superhuman virtue who rarely exists.

Aristocracy

Aristocracy is rule by the virtuous few for the common good; oligarchy is its perversion, where wealth replaces virtue.

Oligarchy

Oligarchy mistakes wealth for virtue and awards political power to the propertied, though wealth does not qualify a man to rule.

God

God is the Unmoved Mover: pure thought thinking itself, the final cause of all motion.

Soul

The soul is the form of a living body: the activity that makes it the living thing it is.

Being

Being is said in many ways, and the primary way is substance: the individual thing that exists in its own right.

Cause

There are four causes (material, formal, efficient, and final), and together they give a complete explanation.

Time

Time is the number of motion with respect to before and after.

Immortality

The active intellect may be eternal, but the individual soul probably perishes with the body.

Theology

Theology is first philosophy: the science of being qua being culminates in the study of the unmoved mover.

Prophecy

Prophetic dreams may have natural causes; divination deserves cautious investigation, not credulous acceptance or dismissive rejection.

Metaphysics

First philosophy studies being as being and its essential attributes; it is the science of the causes and principles of what is.

Chance

Chance is a real but incidental cause: the coincidence of causal lines that might have met otherwise.

Change

Motion is the actuality of what is potential, insofar as it is still potential.

Form

Form is not separate but indwelling: together with matter it constitutes the individual substance, and as actuality it explains what each thing is.

Matter

Matter is potentiality, form is actuality; every physical substance is a composite of the two, and prime matter is the pure capacity to become anything.

Necessity and Contingency

Future contingents are genuinely undetermined; tomorrow's sea-battle is not yet true or false.

One and Many

Being and unity are the same: each substance is a one, and the world is an ordered many.

Space

Place is the innermost motionless boundary of the containing body; there is no void.

World

The world is eternal and uncreated, moved by an unmoved mover who is its final cause but did not make it.

Opposition

Opposites divide into four irreducible kinds: correlatives, contraries, privation and possession, and affirmation and negation.

Relation

Relation is a category of being: relatives are things 'said to be of' or 'toward' something else, though not all relations belong to the furniture of the world.

Same and Other

Sameness is said in several ways: things can be one in number, in species, or in genus, and each kind of identity has its own logic.

Quality

Quality is one of the ten categories of being: it names what a thing is like, from habits and dispositions to colors, shapes, and capacities.

Quantity

Quantity is a category of being: either discrete, like number, or continuous, like a line; it has no contrary and admits of no degrees.

Angel

Beyond the prime mover there are further immaterial movers, one for each celestial sphere, pure intelligences without magnitude.

Eternity

Motion, time, and the heavens are eternal; the Prime Mover is eternal as pure, changeless actuality.

Fate

Not everything that will be is already determined; the future contains genuine contingency.

Infinity

The infinite exists only potentially, never actually: a process that can always go further, never a completed whole.

Truth

Truth is correspondence: saying of what is that it is, and of what is not that it is not.

Knowledge

Knowledge is understanding through causes: grasping why a thing must be as it is.

Mind

Mind becomes all things by receiving their forms: it is potentially everything, actually nothing until it knows.

Experience

Experience gives knowledge of particulars; art and science rise above it to grasp universals and causes.

Will

The will is not a separate faculty but rational desire cooperating with practical reason.

Language

Words are conventional signs of thoughts, which are themselves natural likenesses of things.

Memory and Imagination

Imagination produces images that serve both memory and deliberation, standing between sense and thought.

Rhetoric

Rhetoric is the counterpart of dialectic; persuasion works through character, emotion, and argument.

Opinion

Opinion concerns the contingent; science concerns the necessary; but dialectic, which begins from received opinions, is the gateway to philosophical understanding.

Idea

Ideas are not separate Forms but concepts abstracted by the intellect from sensible things.

Judgment

Judgment is the combination or separation of concepts in a proposition; truth and falsity belong here, not to terms alone.

Sense

Sensation receives the form of the object without its matter; it is the reliable beginning of all knowledge.

Sign and Symbol

Words are conventional symbols of mental experiences, which are themselves natural likenesses of things.

Hypothesis

A hypothesis is the posited existence of a subject, accepted without proof as the starting point from which demonstration proceeds.

Mathematics

Mathematical objects are not separate Forms but properties abstracted from physical things by the mind.

Dialectic

Dialectic reasons from commonly held opinions and is useful for training, debate, and clearing the ground for science, but it is not science itself.

Principle

Principles are the starting points of demonstration, known by induction and intellectual intuition, not by proof.

Reasoning

Reasoning is the syllogism: a discourse in which, certain things being posited, something different necessarily follows.

Logic

Logic is not a science but the instrument of all science: the organon that trains the mind in the formal patterns of demonstration.

Induction

Induction is the intuitive grasp of the universal in the particular; not itself a form of reasoning, it is the cognitive act on which all demonstration depends.

Definition

Definition states the essence: genus plus differentia, capturing the universal nature shared by all members of a species — real definition is a truth about things, not a convention about words.

Universal and Particular

Universals exist only in particular things: the form of man is real, but it exists only in particular human beings and is abstracted from them by the intellect.

Science

Science is demonstrative knowledge from necessary first principles: we know a thing scientifically when we know why it could not be otherwise.

Education

Education forms virtue through habituation, then perfects it with reason.

Nature

Nature is the inner principle of motion and rest in things: each kind striving toward its proper end.

Wisdom

Wisdom is knowledge of first causes and highest principles; practical wisdom is a separate virtue of right action.

Prudence

Prudence is the master virtue of the practical life — the capacity that directs every other virtue toward right action in particular circumstances.

Philosophy

Philosophy begins in wonder and seeks knowledge for its own sake; first philosophy studies being as being.

Man

Man is by nature a rational and political animal, distinguished from all others by the power of speech and moral judgment.

Beauty

Beauty consists in order, symmetry, and definiteness: features we apprehend in well-made things.

Art

Art imitates nature, not by copying, but by completing what nature would do if it could.

Poetry

Poetry is the craft of plot-making; the poet deals in universals, and a convincing impossibility is preferable to an unconvincing possibility.

Progress

Progress in the arts and sciences is cumulative, each generation inheriting from its predecessors; but political life tends to cycle rather than advance toward any final goal.

Life and Death

Life is the activity of self-nutrition and growth; the soul is the form of the living body, not a separable substance.

Animal

The animal is an ensouled body possessing sensation, appetite, and the power of locomotion.

Element

The four elements are defined by paired qualities, and they transform into one another by exchanging them.

Medicine

Health is nature's own achievement; the physician merely removes what stands in nature's way.

Astronomy

The heavens are made of incorruptible matter and move in perfect circles; celestial and terrestrial physics obey fundamentally different principles.

Evolution

Species are eternal natural kinds, each defined by the form it transmits in generation; nature makes nothing in vain.

Mechanics

Every motion requires a cause; bodies move toward their natural places, and the speed of motion is proportional to the force applied and inversely proportional to the resistance of the medium.

Physics

Physics is the science of natural things insofar as they are subject to change; its principles are matter, form, and privation, and its causes are four.