“The hands that help are better far than lips that pray.” — Robert G. Ingersoll

The Freethought Glossary

The vocabulary of reason, defined clearly.

Know a term we should define? Suggest it

A

Abiogenesis
The natural process of life arising from non-living matter. Understanding abiogenesis is central to the scientific worldview and removes the need for a divine creator of life.
Agape
In philosophy and theology, a form of selfless, unconditional love. Secular humanists argue that agape is achievable through empathy and reason without religious motivation.
Agnosticism
Agnosticism is the position that the existence of God, gods, or the supernatural is unknown and perhaps unknowable — that the evidence available to human beings is insufficient to justify either theistic belief or confident atheism.
Animism
The belief that objects, places, and creatures possess a spiritual essence. One of the earliest forms of religious belief, predating organised religion.
Anthropocentrism
The belief that human beings are the central or most important entity in the universe — a view challenged by both science and environmental ethics.
Antitheism
Antitheism is the active opposition to theism — not merely the absence of belief in gods, but the conviction that belief in gods is harmful to individuals and societies and should be challenged.
Apologetics
The systematic defence of a religious position through rational argument. Freethinkers engage with apologetics to identify logical weaknesses in religious claims.
Apostasy
Apostasy is the formal abandonment or renunciation of a religious faith. In many traditions and legal systems, it carries severe social or legal consequences, making it a central concern of freethought advocacy.
Atheism
Atheism is the absence of belief in gods, or the positive assertion that no gods exist — a position that can be arrived at through reasoning about evidence, through philosophical argument, or simply through finding no compelling reason to believe.

B

Blasphemy
Blasphemy is speech or action considered insulting or contemptuous toward the sacred. Blasphemy laws, still enforced in dozens of countries, represent one of the oldest legal mechanisms for suppressing freethought.
Burden of Proof
The obligation to provide evidence for a claim. In freethought, the burden of proof lies with the person making the positive claim — including claims about the existence of God.

C

Categorical Imperative
Kant's moral principle that one should act only according to rules that could be universalised — a secular foundation for ethics independent of divine command.
Censorship
The suppression of speech, writing, or ideas deemed objectionable by authorities. The history of censorship is inseparable from the history of freethought.
Church-State Separation
The principle that government and religious institutions should operate independently of each other — that the state should neither promote nor inhibit religion.
Cogito
The cogito (I think, therefore I am) is Descartes' foundational argument that the act of doubting one's own existence proves that one exists as a thinking being.
Compatibilism
Compatibilism is the position that free will and determinism are not mutually exclusive — that meaningful human choice is possible even in a universe governed entirely by causal laws.
Consequentialism
The ethical theory that the morality of an action is determined solely by its consequences — the family of theories that includes utilitarianism.
Cosmological Argument
A family of arguments for God's existence based on the claim that the universe must have a cause or explanation — and that this cause must be God.
Cosmology
The scientific study of the origin, structure, and fate of the universe. Modern cosmology has replaced religious creation narratives with evidence-based models.
Creationism
Creationism is the belief that the universe and life were created by a supernatural being, typically as described in a religious text, in direct conflict with evolution and cosmology.
Critical Thinking
The disciplined process of analysing and evaluating information and arguments to form reasoned judgements — the practical application of philosophical skepticism.
Cultural Relativism
The principle that beliefs and practices should be understood in terms of their own culture. Distinct from moral relativism, it is a methodological stance rather than an ethical one.

D

Deconversion
Deconversion is the process of losing one's religious faith — often gradual, sometimes traumatic, involving a fundamental re-evaluation of identity, community, and moral framework.
Deism
Deism is the belief that a creator God can be known through reason and observation of the natural world, but that this God does not intervene in human affairs, has not revealed himself through scripture, and is not available for prayer or worship.
Deontology
The ethical framework that judges the morality of actions based on rules and duties rather than consequences — associated with Kant and often contrasted with utilitarianism.
Design Argument
The argument from design claims that complexity and apparent purpose in nature is evidence of an intelligent designer. It was dismantled by Hume and rendered unnecessary by Darwin.
Determinism
Determinism is the metaphysical doctrine that every event, including every human thought and action, is the inevitable consequence of prior events and the laws of nature — that given the state of the universe at any moment, only one future is possible.
Dogma
A set of beliefs held as authoritatively true by a group, not open to question or revision. The rejection of dogma — in favour of evidence and argument — is the defining commitment of freethought.
Dualism
The metaphysical view that mind and body are fundamentally different kinds of substance — that consciousness is non-physical. Most freethinkers reject dualism in favour of physicalism.

E

Empiricism
Empiricism is the philosophical doctrine that all genuine knowledge of the world derives from sensory experience, and that the mind brings no innate content to experience that can serve as a foundation for substantive knowledge.
Epistemology
The branch of philosophy concerned with the nature, sources, and limits of knowledge — the study of what we can know, how we can know it, and what justifies our beliefs.
Establishment Clause
The provision of the First Amendment to the US Constitution that prohibits the government from establishing an official religion or favouring one religion over another.
Ethics
The philosophical study of right and wrong conduct. Secular ethics holds that moral principles can be grounded in reason, empathy, and human well-being without reference to divine command.
Euthyphro Dilemma
Plato's challenge to divine command theory: is something good because God commands it, or does God command it because it is good? Either answer undermines the claim that morality requires God.
Evolution
Evolution by natural selection is the scientific explanation for the diversity of life on Earth — the process by which populations change over generations through variation, inheritance, and differential survival.
Existentialism
The philosophical tradition that emphasises individual existence, freedom, and choice — holding that human beings define their own meaning in a universe that provides none inherently.

F

Faith
Faith, in its religious sense, is belief without sufficient evidence — or belief maintained in spite of contrary evidence. Freethinkers distinguish it sharply from trust, which is earned through experience.
Fallacy
An error in reasoning that renders an argument invalid or unsound. Recognising common fallacies — ad hominem, straw man, appeal to authority, false dilemma — is a core skill of critical thinking.
Falsifiability
Karl Popper's criterion for distinguishing science from non-science: a claim is scientific only if it could, in principle, be proven false by observation or experiment.
Fideism
The view that faith is independent of reason, or even opposed to it — that religious belief should be held despite the absence of rational justification.
Free Exercise Clause
The provision of the First Amendment that protects individuals' right to practise their religion — or to practise no religion — without government interference.
Free Will
The capacity of agents to choose between possible courses of action. Whether free will is compatible with a deterministic universe is one of philosophy's oldest debates.
Freethought
Freethought is the practice of forming beliefs about religion, ethics, and metaphysics on the basis of reason and evidence rather than tradition, authority, or revelation.

G

Gnosticism
An ancient set of religious ideas emphasising special spiritual knowledge (gnosis). In modern usage, contrasted with agnosticism to describe certainty about metaphysical claims.

H

Hedonism
The philosophical view that pleasure or happiness is the highest good. Often caricatured as self-indulgence, philosophical hedonism is a serious ethical position.
Heresy
Belief or opinion that contradicts the established doctrines of a religious institution. The history of heresy prosecutions is, in large part, the history of freethought under persecution.
Humanism
A philosophical stance that emphasises the value and agency of human beings and the use of reason and evidence as the basis for understanding the world and making ethical decisions.

I

Ignosticism
The position that the question of God's existence is meaningless until the term God is coherently defined — a prerequisite challenge to both theism and atheism.
Indoctrination
The process of teaching a person to accept a set of beliefs uncritically. Freethinkers distinguish education (which encourages questioning) from indoctrination (which forbids it).
Intelligent Design
The claim that certain features of the natural world are best explained by an intelligent cause rather than natural selection — widely regarded by scientists as repackaged creationism.

L

Logical Positivism
The philosophical movement that held only statements verifiable through empirical observation or logical proof are meaningful — rendering most theological claims literally meaningless.

M

Materialism
Materialism is the metaphysical doctrine that everything that exists is physical — that matter and energy, interacting according to natural laws, constitute the whole of reality, and that mind, consciousness, and apparently non-physical phenomena are ultimately physical phenomena under other descriptions.
Metaphysics
The branch of philosophy that investigates the fundamental nature of reality — including questions about existence, causation, time, space, and the relationship between mind and matter.
Methodological Naturalism
The principle that scientific investigation should assume natural causes for natural phenomena — distinct from philosophical naturalism, which makes no claims beyond method.
Monotheism
The belief in a single God. The dominant form of theism in Christianity, Islam, and Judaism, and the primary target of most freethought criticism.
Moral Realism
The view that there are objective moral facts independent of what anyone believes — that some actions are genuinely right or wrong regardless of cultural or personal opinion.
Moral Relativism
The view that moral judgements are not universally valid but are relative to cultural, historical, or individual perspectives. Most secular ethicists reject strong relativism.

N

Naturalism
The philosophical view that the natural world is all there is — that there are no supernatural entities, forces, or realms, and that everything can in principle be explained by natural causes.
Nihilism
The philosophical position that life has no inherent meaning, purpose, or value. More precisely the rejection of imposed meaning — which can be either paralysing or liberating.
Nones
People who identify with no religion when asked about their religious affiliation. The fastest-growing demographic in religious surveys across the Western world.

O

Occam's Razor
The principle that among competing explanations, the one that makes the fewest assumptions should be preferred — a foundational tool of scientific and philosophical reasoning.
Ontological Argument
An attempt to prove God's existence through pure reason alone — arguing that the concept of a maximally great being entails its existence. Most philosophers consider it unsound.
Ontology
The branch of philosophy concerned with what exists — the study of being, existence, and the categories of things that are.

P

Pantheism
Pantheism is the metaphysical view that God and the universe are identical — that there is no transcendent creator standing apart from creation, but that the totality of nature is itself divine.
Pascal's Wager
The argument that it is rational to believe in God because the potential gain (eternal salvation) outweighs the potential loss. Critics note it assumes a single God and ignores sincerity.
Phenomenology
The philosophical study of consciousness and subjective experience — examining how things appear to us rather than what they are in themselves.
Physicalism
The thesis that everything that exists is physical, or supervenes on the physical — that there are no irreducibly mental, spiritual, or supernatural properties in the world.
Pluralism
The recognition and affirmation of diversity within a society — the principle that multiple worldviews can coexist, and that no single perspective has a monopoly on truth.
Polytheism
The belief in or worship of multiple gods. The dominant form of religion through most of human history, before the rise of monotheism.
Positivism
The philosophical system holding that knowledge should be based on natural phenomena verified by empirical methods — rejecting metaphysical and theological speculation.
Pragmatism
The philosophical tradition that evaluates ideas by their practical consequences rather than their correspondence to abstract truth — associated with James, Dewey, and Peirce.
Problem of Evil
The challenge of reconciling an omnipotent, omniscient, and benevolent God with the existence of suffering — widely considered the strongest argument against classical theism.
Proselytism
The practice of attempting to convert others to one's own religion or belief system. Freethinkers generally oppose proselytism while defending the right to express and discuss beliefs.

R

Rationalism
Rationalism is the philosophical position that reason, independent of sensory experience, is the primary source of knowledge — and that the most important truths about reality are those that can be arrived at through pure thought.
Reductionism
The view that complex phenomena can be explained by reducing them to simpler, more fundamental components — a methodological approach central to science.
Relativism
The broad philosophical position that truth, knowledge, or morality is not absolute but varies according to perspective, culture, or historical context.

S

Scientism
The view that science is the only reliable source of knowledge. Used both as a self-description by some freethinkers and as a criticism by their opponents.
Secular Ethics
Moral frameworks that do not depend on religious authority or supernatural belief — grounded instead in reason, empathy, human rights, and consequences.
Secular Humanism
Secular humanism is a philosophical life stance that affirms human dignity, reason, and ethics without reference to the supernatural — holding that human beings can live well and act rightly on the basis of natural capacities alone.
Secularism
The principle that government and public institutions should be independent of religious influence — neutral on matters of religion while protecting freedom of belief.
Skepticism
Skepticism is the philosophical position that holds that knowledge claims — particularly those about the external world, God, morality, or the past — require scrutiny, and that many claims commonly accepted as knowledge fail to meet the standards that genuine knowledge demands.
Social Contract
The theory that political authority is derived from an agreement among individuals to form a society — a secular foundation for governance associated with Hobbes, Locke, and Rousseau.
Solipsism
The philosophical position that only one's own mind is sure to exist — that the external world and other minds cannot be known with certainty.

T

Theism
The belief in the existence of at least one god, typically a personal God who creates, sustains, and intervenes in human affairs.
Theodicy
The attempt to justify God's goodness in the face of evil and suffering. Freethinkers generally regard theodicies as unsuccessful.

U

Utilitarianism
The ethical theory that the right action is the one that produces the greatest good for the greatest number — a secular moral framework developed by Bentham and Mill.