Key Philosophical Concepts: Definitions and Explanations

Key Philosophical Concepts

Material Cause: The matter, stuff, or substance of which something is made. One of Aristotle’s four causes.

Materialism: The metaphysical view that all reality consists of material or physical entities with their physical properties. Contrasted with Idealism.

Monism: The metaphysical view that all reality is one. Idealism and Materialism are examples of monism.

Moral Argument: A proof for the existence of God; God’s existence is the only adequate grounds to explain objective morality.

Naturalism: The belief that physical nature is the only reality. The philosophy of naturalism is characterized by Monism, antisupernaturalism, scientism, and Humanism.

Nihilism: The view that there is no meaning, purpose, significance, or value in the universe.

Noetic: Pertaining to reason, knowledge, and the intellect.

Objective Idealism: The belief that things genuinely exist apart from our perception of them.

Ockham’s Razor: The explanation which fits the facts with the least assumptions is the best. Also known as the principle of parsimony.

Thomism: Of or pertaining to the philosophical and theological thought of St. Thomas Aquinas (1225-1274).

Transcendent: Beyond, or distinct from, the time/space world.

Weltanschauung: German term, referring to a person’s world view (a conceptual scheme for interpreting reality).

Ontological Argument: A proof for the existence of God; St. Anselm argued that reflection on God’s perfect essence (or being) actually necessitates His existence.

Ontology: The study of being; often used interchangeably with Metaphysics.


Pantheism: A world view that makes God identical with the world; “All is God and God is all.” God is wholly Immanent, and therefore not transcendent.

Phenomena: In Kant, the world of appearance (how things appear to the senses); as opposed to the Noumena (world of reality). Also referred to as the phenomenal world.

Philosophy: Literally, the “love of wisdom”; an attempt to provide rational and coherent understanding of the fundamental questions of life.

Platonism: Of or pertaining to the philosophy of Plato (427-347 B.C.)

Pluralism: The metaphysical view that ultimate reality consists of many things. Contrasted with Monism.

Pragmatism: An American philosophy which makes workability and practical consequences the test for truth.

Rationalism: Broadly speaking, the epistemological view that stresses reason as the test of truth. In a strict sense, the belief that at least some knowledge is acquired independent of sense experience. Contrasted with Empiricism.

Realism: The metaphysical view that asserts that physical objects exist apart from being perceived; the belief that the essences of things possess objective reality.

Relativism: The belief that no absolutes exist (in truth and/or ethics). Truth and morality vary from person to person, time to time, circumstance to circumstance.

Skepticism: In a loose sense, to doubt, question, or suspend judgment on philosophical issues. In a strict sense, to deny that true knowledge is attainable.

Socratic Method: Derived from the Greek philosopher Socrates, a method for finding truth and meaning through rigorous questioning.

Solipsism: “I myself only exist.” The only reality that exists is one’s self.

Subjective Idealism: The belief that things (ideas) are dependent upon perception for their particular existence.

Substance: A thing’s underlying essence; that which makes a thing what it is.

Tabula Rasa: Literally, a “blank tablet”. John Locke’s empirical view that human beings possess no innate (inborn) ideas or principles.