Significant Metaphysical Concepts

Why This Matters

Modern philosophy's metaphysical debates aren't just abstract puzzles—they're the foundation for everything else you'll encounter in this course. When Descartes asks whether mind and body are separate substances, he's setting up centuries of debate about consciousness, personal identity, and the limits of scientific explanation. When Hume challenges our assumptions about causality, he's forcing us to reconsider what we can actually know versus what we merely believe. These concepts form the scaffolding that supports discussions of ethics, political philosophy, and philosophy of science.

You're being tested on your ability to trace how these ideas connect, conflict, and evolve across thinkers. The exam won't just ask you to define "empiricism"—it will ask you to explain how Locke's tabula rasa challenges Descartes' innate ideas, or why Berkeley's idealism is actually a form of empiricism despite seeming so different from Locke's materialism. Don't just memorize definitions—know what problem each concept was trying to solve, who championed it, and what objections it faced.

---

The Substance Question: What Is Reality Made Of?

The most fundamental metaphysical question asks what stuff exists. Modern philosophers split into camps based on whether they believed reality consists of one type of substance, two types, or whether "substance" is even a coherent concept. This debate shapes every other philosophical question about mind, knowledge, and causation.

Substance

• The underlying "what" of existence—substance refers to whatever persists through change and serves as the bearer of properties
• Aristotelian inheritance shaped early modern debates, with philosophers asking whether substances are material, mental, or something else entirely
• Identity and change depend on this concept; understanding what makes something the same thing over time requires a theory of substance

Dualism

• Two distinct substances exist: mind and body—René Descartes argued that mental substance (thinking) and physical substance (extension) are fundamentally different
• The interaction problem immediately arises: if mind and body are completely different kinds of stuff, how can your decision to raise your arm actually move your physical arm?
• Cartesian dualism set the agenda for modern philosophy of mind, even as most subsequent thinkers tried to overcome it

Materialism

• Only physical matter exists—everything, including thoughts and consciousness, can ultimately be explained through physical processes
• Thomas Hobbes championed this view against Descartes, arguing that even reasoning is just "computation" happening in the brain
• Scientific worldview alignment makes materialism influential today, though it struggles to explain subjective experience (qualia)

Idealism

• Reality is fundamentally mental—George Berkeley argued that material objects only exist as perceptions in minds (esse est percipi: to be is to be perceived)
• Berkeley's target was skepticism—by eliminating matter, he thought he could guarantee that our perceptions accurately represent reality (since perceptions are reality)
• God's perception ensures objects continue to exist when no human observes them, making Berkeley's idealism surprisingly theistic

Monism

• One fundamental substance underlies all reality—this rejects dualism's division between mind and body
• Spinoza's version identifies this single substance with God/Nature, where mind and body are just different attributes of the same thing
• Dissolves the interaction problem by denying that mind and body are truly separate, though it raises questions about individual identity

---

The Mind-Body Problem: How Do Thought and Matter Connect?

Descartes' dualism created a puzzle that dominated modern philosophy: if mind and body are different substances, how do they causally interact? Every major philosopher after Descartes had to offer some solution—or reject the problem's premises entirely.

Mind-Body Problem

• The central puzzle of Cartesian philosophy—how can an immaterial mind cause physical effects (like moving your hand) and how can physical events cause mental experiences (like feeling pain)?
• Occasionalism (Malebranche) and pre-established harmony (Leibniz) offered solutions that invoked God as intermediary
• Personal identity questions emerge here: if your mind and body are separate, which one is the "real" you?

Determinism

• All events are caused by prior events—this includes human thoughts and actions, which are products of preceding physical or mental states
• Spinoza and Leibniz both endorsed versions of determinism, seeing the universe as a rationally ordered system where everything follows necessarily
• Moral responsibility becomes problematic: if your actions were determined before you were born, can you be praised or blamed for them?

Free Will

• The capacity to choose independently of determining causes—this concept is essential for moral responsibility and human dignity
• Libertarian free will (not the political kind) claims some human choices are genuinely undetermined; compatibilism argues free will is compatible with determinism
• Kant later argued that we must assume free will for morality to make sense, even if we can't prove it theoretically

---

Sources of Knowledge: Rationalism vs. Empiricism

The epistemological debate between rationalists and empiricists asks where knowledge comes from. Do we have built-in concepts that reason can access, or does all knowledge arrive through the senses? This division structures the entire early modern period.

Epistemology

• The study of knowledge itself—asks what knowledge is, how we get it, and what its limits are
• Justified true belief was the traditional definition, though modern philosophers (especially after Hume) questioned whether justification is ever certain
• Foundationalism vs. coherentism debates emerge here: does knowledge rest on self-evident foundations, or on a web of mutually supporting beliefs?

Rationalism

• Reason is the primary source of knowledge—Descartes, Spinoza, and Leibniz argued that the most certain truths come from intellectual insight, not sensory observation
• Innate ideas and a priori knowledge are central; some concepts (like God, infinity, or mathematical truths) can't come from experience
• Deductive reasoning from self-evident premises yields certainty that empirical observation can never match

Innate Ideas

• Certain concepts are built into the mind from birth—Descartes argued that ideas like God, substance, and mathematical truths are innate, not learned
• The "trademark argument" claims the idea of an infinite, perfect God couldn't originate from finite, imperfect human experience
• Leibniz refined this with his notion of "petites perceptions"—innate ideas exist but may require experience to bring them to conscious awareness

Empiricism

• All knowledge derives from sensory experience—Locke, Berkeley, and Hume rejected innate ideas and grounded knowledge in observation
• The mind processes sensory data through reflection, building complex ideas from simple impressions
• Scientific method alignment made empiricism influential, though it struggled to explain mathematical and logical knowledge

Tabula Rasa

• The mind begins as a "blank slate"—John Locke's famous metaphor denies that any ideas are innate
• Experience writes on the slate through sensation (external experience) and reflection (internal awareness of mental operations)
• Political implications follow: if humans aren't born with fixed natures, education and environment become crucial for shaping character

Skepticism

• Certain knowledge may be impossible—skeptics challenge our ability to know anything with absolute certainty
• Descartes used skepticism methodologically (doubting everything to find what can't be doubted), while Hume's skepticism was more genuine
• The problem of induction (Hume) shows we can't rationally justify believing the future will resemble the past—a devastating challenge to empiricism from within

---

Causation and Natural Order

Understanding how causes produce effects is essential for both science and philosophy. Modern philosophers disagreed sharply about whether causal connections are necessary truths we can know through reason, or merely patterns we observe through experience. Hume's challenge to causation remains one of philosophy's most influential arguments.

Causality

• The relationship between cause and effect—understanding this relationship is fundamental to science, ethics, and metaphysics
• Hume's devastating critique argued that we never perceive necessary connections; we only see constant conjunction (one event regularly following another)
• Custom and habit explain our belief in causation, not rational insight—this makes causal knowledge psychologically inevitable but philosophically unjustified

---

Quick Reference Table

---

Self-Check Questions

1. Both materialism and idealism are forms of monism that reject Cartesian dualism. What distinguishes them, and why might Berkeley's idealism seem counterintuitive despite solving certain philosophical problems?

2. Explain how Hume's skepticism about causation poses a challenge specifically to empiricism, even though Hume himself was an empiricist. What does this reveal about the limits of grounding knowledge in experience?

3. Compare and contrast innate ideas (Descartes/Leibniz) with tabula rasa (Locke). If you had to defend one position on an FRQ, what would be the strongest argument for each side?

4. How does the mind-body problem arise from Descartes' dualism, and why did subsequent philosophers like Spinoza and Leibniz feel compelled to offer alternative metaphysical systems?

5. A free-response question asks you to evaluate whether determinism is compatible with moral responsibility. Which philosophers would you cite for the view that they're incompatible, and which would you cite for compatibilism?