Philosophy is often described as a conversation that has spanned millennia, connecting the greatest minds of history. However, stepping into this conversation can sometimes feel like entering a room where everyone is speaking a secret language. Words like “validity,” “substance,” and “idealism” often carry very different meanings in a philosophical text than they do in everyday conversation.
To help you navigate the landscape of logic, ethics, and metaphysics, I have compiled this comprehensive glossary.
Here are the essential terms you need to know, from Aesthetics to Zombies.
A
Aesthetics A branch of philosophy concerned with what is considered beautiful or artistic.
Analytic proposition The opposite of a synthetic proposition—one that is true by virtue of the meaning of the words used to express it, such as “All stallions are male.”
Anthropomorphism Attributing human behavior or characteristics to something that is not human, such as an animal.
Arete In ancient Greek philosophy, this comprises excellence and virtue.
Argument In logic, a process of reasoning that infers a conclusion from one or more premises. The premises are supposed to support the conclusion.
C
Conclusion The final part of a logical argument that is inferred from the premises.
Consequentialism The view in moral philosophy that the morality of an action should be judged on its outcomes.
Contingent truth Something that may or may not be the case—the opposite of a necessary truth.
Contradictory Two statements are contradictory when the truth/falsity of one entails the falsity/truth of the other. If one is true, the other must be false.
Contrary Two statements are contrary if they cannot both be true, but they may both be false.
D
Deduction Drawing a particular conclusion from a general rule. An argument based on deduction is always valid, unlike its opposite, induction.
Dialectic In ancient Greece, a method of pursuing truth by discussing ideas with people holding differing views.
Dualism The view that there are two kinds of substances.
E
Empiricism The belief that all knowledge of things outside the mind is acquired through sense experience.
Entail In logic, when one thing inevitably follows from another.
Epistemology The branch of philosophy concerned with what knowledge is, what we can know, and how we can know what we know.
Essence The true nature of something—what makes it what it is.
Ethics The study of right and wrong behavior and the moral principles that govern that behavior. Also known as moral philosophy.
Existentialism An approach in 20th-century philosophy that focuses on human existence and the search for meaning or purpose in life.
F
Fallacy An error of reasoning that is easily made.
Falsifiability A statement, or set of statements, is said to be falsifiable if it can be shown to be false.
Fuzzy logic A system of logic that deals with half-truths, allowing them to be expressed on a continuum between true and false.
H
Half-truth A claim that is partially true.
Harm principle Proposed by John Stuart Mill, the idea that people should be free to do what they want, provided this does not harm others, or restrict their freedom to do the same.
Hypothesis A proposed explanation that is to be investigated further.
I
Idealism The view that reality consists ultimately of minds and their ideas, rather than material things. The opposite view is materialism.
Induction Inferring a conclusion from one or more premises; the conclusion is supposed to be supported but not logically entailed by the premises.
Inference A conclusion drawn by means of an argument from premises.
L
Liberalism In political philosophy, the view that society should protect individual freedom and equality.
Logic The branch of philosophy that studies rational argument—including how to construct a good argument and identify flaws in arguments.
Logical form In logic, the structure of an argument.
M
Materialism The idea that ultimately everything is material. There are no nonmaterial substances or properties. The opposite view is idealism.
Metaphysics The branch of philosophy concerned with the fundamental nature of reality.
Mind-body dualism The view that mind and body are two separate substances.
Monism The view that there is ultimately just one substance.
Moral philosophy Also known as ethics, the branch of philosophy that examines ideas of right and wrong, good and bad, and the moral basis for our actions and judgments.
Morality Principles that determine right and wrong, or good and bad behavior.
N
Necessary truth Something that must be the case—the opposite of a contingent truth.
Noumenon A thing-in-itself, which exists independently of our experience, beyond the scope of our minds—the opposite of phenomenon.
P
Paradox An argument, which, despite apparently sound reasoning from acceptable premises, leads to a conclusion that seems absurd.
Phenomenon Something that we can experience. This is the opposite of noumenon.
Philosophy of mind The branch of philosophy that studies the nature of the mind, mental processes, consciousness, and the relationship of the mind to the physical body.
Physicalism The belief that ultimately everything is physical. For example, our mental experiences can be explained through the physical workings of our brains.
Pineal gland A tiny gland in the brain that looks like a pine cone. René Descartes believed this to be the point where the mind connects to the body.
Political philosophy The branch of philosophy that examines the nature and methods of the state, including the concepts of justice, politics, and social order.
Pragmatism A philosophical approach that emphasizes the usefulness of knowledge—a theory or belief is successful if it can be practically applied.
Premise The starting point of an argument. Any argument must start from at least one premise—for example, “All men are mortal.”
Primary and secondary qualities In the philosophy of John Locke, an object has primary qualities, which can be measured independently of experience—such as size—and secondary qualities, which are determined by personal experience of that object—such as color.
Proof An argument that establishes the truth of its conclusion beyond doubt.
Property dualism The notion that physical things have nonphysical properties, such as mental properties.
Proposition What is asserted when one makes a claim. Propositions can be true or false.
R
Rational Based on, or at least not contrary to, the principles and use of logic and reason.
Rationalism The belief that all knowledge is acquired through rational thought, or reasoning. The opposite view is known as empiricism.
Reasoning Thinking about something in a logical, rational way.
Relativism The notion that what is true or false depends upon cultural, social, or historical context.
S
Skepticism The view that we do not or cannot have knowledge in a particular area. For example, skeptics about the external world say that we cannot know about the world outside our own minds.
Social contract When members of a society implicitly agree to cooperate in order to achieve goals that benefit the group as a whole, sometimes at the expense of individuals within it.
Soul The spiritual, immaterial part of a being, which is supposed to live on after death.
Substance Something that is capable of existing on its own. For example, a mental substance could exist on its own, without any physical substance. Materialists say there is just one kind of substance—material substance. Dualists claim there are two kinds of substances: mental and physical.
Syllogism A form of reasoning in which a conclusion is drawn from two premises. An example of a syllogism is: “All men are mortal. Socrates is a man. Therefore, Socrates is mortal.”
Synthetic proposition A proposition that is not true by virtue of the meanings of the words used to express it. The opposite is an analytic proposition.
T
Thing-in-itself What a thing actually is, rather than what it is as perceived through our senses. Another term for noumenon.
Thought experiment An imaginary situation that is conceived for the purpose of testing a hypothesis.
Truth of fact A true statement that cannot be established by reason alone (unlike a truth of reasoning).
Truth of reasoning A statement that can be established as true through reason alone—unlike a truth of fact.
U
Utilitarianism A theory in moral and political philosophy that judges the morality of an action by its consequences, and regards the most desirable outcome as the greatest good for the greatest number of people.
V
Validity An argument is said to be valid if its conclusion follows logically from its premises. This does not mean that the conclusion is true.
Verifiability A statement can be verified if it can be shown to be true.
W
World In philosophy, the words world, universe, and cosmos are often used to mean the whole of reality that we can experience. Philosophers also sometimes refer to different “worlds,” such as the phenomenal world, or the noumenal world.
World of ideas (or forms) According to Plato, a world, separate from the world we live in, that contains ideal forms of things. We only ever see imperfect reflections of these perfect forms.
Z
Zombie In philosophy, a person who looks and behaves like a normal human, but who has no consciousness.
