Metaphysics and Ontology
Metaphysics asks what exists, what it means to exist, and what basic categories reality contains; ontology is the inventory of being. GCE questions usually target substance, universals, causation, identity and change, and freedom and determinism.
Substance and properties
A substance is traditionally that which exists in itself and bears properties, rather than being a property of something else. Aristotle treats primary substances as concrete individuals, with form and matter; Descartes distinguishes thinking and extended substances; Locke posits a substratum underlying qualities. Bundle theories deny an underlying bearer, reducing a thing to a cluster of properties. The debate matters because it shapes claims about persistence and change.
Universals
The problem of universals asks what makes many particulars share a property. Plato's Forms are separate, eternal, perfect paradigms; particulars 'participate' in them. Aristotle holds universals immanent in particulars: redness exists in red things, not in a separate realm. Nominalism denies real universals: only particulars exist, and general words are names or concepts. Conceptualism locates universals in the mind.
Causation and freedom
Hume argues that we observe constant conjunction, not necessary connection; causation is a habit of the mind. Determinism says every event has a cause; fatalism says outcomes are fixed regardless of what we do. Compatibilism reconciles determinism with freedom by defining freedom as acting on one's own desires without external constraint; libertarianism requires genuine alternative possibilities; hard determinism denies free will.
Identity and change
The Ship of Theseus: if every plank is replaced, is it the same ship? Substance theorists appeal to form or continuity; bundle theorists to psychological or causal continuity; four-dimensionalists to temporal parts.
Worked example
'This tomato and that tomato are both red.' If redness is a separate entity, it seems to be in many places at once. Plato explains this by a separate Form in which both participate. Aristotle replies that redness is one universal instantiated in each tomato, so it is not a separate thing. A nominalist replies that only particular red surfaces exist; 'red' is a word we apply by resemblance. The reasoning turns on whether a shared predicate commits us to a shared entity.
Traps
Do not equate substance with physical matter. Determinism is not fatalism: fatalism denies that actions can alter outcomes, while determinism says events are caused. Hume did not simply deny causation; he redefined it as constant conjunction plus mental expectation. Identity over time is not the same as sameness of material parts.