Key Metaphysical Theories

Why This Matters

Metaphysics is the backbone of philosophy—it asks the biggest questions you can ask: What exists? What is real? What am I? When you study metaphysical theories, you're not just memorizing positions; you're learning the frameworks philosophers use to make sense of everything from consciousness to causation. These theories show up constantly in discussions of free will, personal identity, philosophy of mind, and ethics. If you can't explain the difference between dualism and materialism, you'll struggle to follow debates about whether minds are just brains.

Here's what you're really being tested on: the ability to identify what kind of claim a philosopher is making about reality and why it matters for other philosophical problems. Don't just memorize that Descartes was a dualist—know what problem dualism tries to solve and what problems it creates. Each theory below illustrates a fundamental choice about the nature of existence, and exam questions will ask you to compare, contrast, and apply these frameworks to new scenarios.

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Theories of Substance: What Exists?

The most basic metaphysical question is deceptively simple: what kind of stuff is reality made of? These theories offer competing answers, and your choice here shapes everything else in your philosophical worldview.

Materialism

• Only physical matter exists—everything from thoughts to emotions can ultimately be explained through physical processes and natural laws
• Rejects immaterial substances like souls, spirits, or non-physical minds; consciousness is just brain activity
• Associated with scientific worldviews—thinkers like Karl Marx applied materialist thinking to history and society

Idealism

• Reality is fundamentally mental—what we call "physical objects" are actually ideas or perceptions in minds
• George Berkeley's famous claim: esse est percipi (to be is to be perceived); objects exist only as they're experienced
• Immanuel Kant's twist—we can never know "things in themselves," only how they appear to our minds

Dualism

• Two distinct substances exist: mental (mind/soul) and physical (body/matter)
• The mind-body problem—if mind and body are different substances, how do they interact? How does a non-physical thought move a physical arm?
• Descartes is the key figure—his Meditations argues that thinking proves the mind exists, but the body is a separate extended substance

Monism

• Only one kind of substance exists—this is the umbrella term for both materialism and idealism
• Spinoza's version argues that God and Nature are the same single substance, with mind and matter as two attributes of it
• Resolves dualism's interaction problem by denying there are two separate things to interact

Pluralism

• Multiple irreducible substances or realities exist—reality can't be collapsed into just one or two categories
• William James championed this view—experience is too rich and varied to fit neat metaphysical boxes
• Emphasizes complexity over simplicity—sometimes the messier answer is the more honest one

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The Problem of Universals: Do Abstract Things Exist?

When you say two red apples share "redness," does that redness exist somewhere? This ancient debate shapes how we think about language, mathematics, and scientific laws.

Realism

• Universals exist independently—properties like "redness" or "triangularity" are real things, not just labels we invented
• Contrasts with idealism (confusingly named!)—here "realism" means the external world exists independently of our minds
• Different varieties: scientific realism says theoretical entities (electrons, genes) really exist; moral realism says ethical truths are objective

Nominalism

• Only particular objects exist—there's no such thing as "redness," just individual red things
• General terms are just names (nomina in Latin) we use for convenience; they don't refer to real universal entities
• William of Ockham's razor—don't multiply entities beyond necessity; if we can explain language without universals, we should

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Free Will and Determinism: Are We Free?

These theories address whether human choices are genuinely free or whether everything—including your decision to study philosophy—was inevitable. This debate connects directly to moral responsibility and ethics.

Determinism

• All events are caused by prior events—given the state of the universe a moment ago, only one future is possible
• Implies free will is illusory—your "choices" are just the inevitable results of brain states, which were caused by prior states
• Comes in varieties: causal determinism (physics), theological determinism (God's foreknowledge), logical determinism (future truths already fixed)

Free Will

• Agents can genuinely choose between alternatives—your decisions aren't fully determined by prior causes
• Central to moral responsibility—if you couldn't have done otherwise, how can we blame or praise you?
• Libertarian free will (not the political kind) says some human actions are uncaused or self-caused

Compatibilism

• Free will and determinism can both be true—freedom doesn't require the ability to have done otherwise
• Redefines freedom as acting according to your own desires without external coercion, even if those desires were determined
• Hume and Dennett argue that this is the only coherent notion of freedom; "libertarian" free will is incoherent

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Approaches to Knowledge and Experience

These theories blur the line between metaphysics and epistemology, asking how the nature of reality shapes what we can know. They're often tested together.

Empiricism

• Knowledge comes from sensory experience—the mind starts as a "blank slate" (tabula rasa) written on by experience
• Locke, Berkeley, and Hume are the British Empiricists; each pushed the view in more radical directions
• Challenges innate ideas—nothing is "built in" to the mind; even concepts like causation come from observed patterns

Rationalism

• Reason is the primary source of knowledge—some truths can be known through pure thinking, independent of experience
• Emphasizes innate ideas—Descartes argued we're born with concepts like God, infinity, and mathematical truths
• Descartes, Spinoza, Leibniz are the Continental Rationalists; they trusted deductive reasoning over unreliable senses

Phenomenology

• Studies consciousness from the first-person perspective—describes how things appear to us before theorizing about what they "really" are
• Husserl's method: "bracket" assumptions about the external world and focus purely on the structure of experience
• Heidegger extended this to ask about the meaning of Being itself—what does it mean for anything to exist?

Pragmatism

• Truth is what works—evaluate beliefs by their practical consequences, not abstract correspondence to reality
• Rejects metaphysical debates that have no practical difference; if two theories predict the same outcomes, the dispute is meaningless
• Peirce, James, Dewey developed this distinctly American philosophy; it influenced everything from education to law

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Existence and Meaning: The Human Condition

These theories focus specifically on human existence—what it means to be a conscious, choosing being thrown into a world we didn't create.

Existentialism

• Existence precedes essence—you aren't born with a fixed nature; you create yourself through your choices
• Radical freedom brings anxiety—with no predetermined purpose, you're fully responsible for who you become
• Sartre and de Beauvoir explored how this freedom operates in contexts of oppression, bad faith, and authentic living

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Quick Reference Table

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Self-Check Questions

1. Both materialism and idealism are forms of monism. What do they share, and what fundamental claim separates them?

2. A neuroscientist argues that "decisions" are just brain states caused by prior brain states, so moral blame is unjustified. Which metaphysical position does this reflect, and how would a compatibilist respond?

3. Compare nominalism and realism on this question: when mathematicians discover a new theorem, are they inventing or discovering something?

4. Descartes' dualism faces the "interaction problem." Explain the problem and identify one alternative theory that avoids it.

5. An existentialist and a determinist are debating whether a person who grew up in poverty and turned to crime is morally responsible. Outline how each would argue their position and where they fundamentally disagree.