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Truthmaker theory holds that for every truth there must be some entity in the world — a truthmaker — whose existence necessitates that truth. The classic candidate truthmakers are facts or states of affairs: structured entities composed of objects and properties bound together. Armstrong championed the view that facts are irreducible additions to ontology — the world is not just a collection of objects and properties floating free, but objects-having-properties. This grounds the correspondence intuition: the proposition 'the cat is on the mat' is true because there exists a fact (the cat's being on the mat). Critics question whether truthmaker maximalism is sustainable, especially for negative truths ('there are no unicorns') and universal truths.
Read Armstrong's Truth and Truthmakers chapters 1-3, then study Molnar's and Parsons's objections regarding negative existentials. Try to construct a truthmaker for the claim 'there are no hobbits' — the difficulty is instructive.
The truthmaker project begins with a simple intuition: truth cannot "float free" of the world. If a proposition is true, there must be something in reality that makes it true — something that accounts for its truth rather than merely correlating with it. From your study of ontological categories, you know the landscape of what kinds of things might exist. From universals and particulars, you know how properties and objects relate. Truthmaker theory ties these together by asking: what in the ontological inventory *grounds* true propositions?
The classic answer identifies truthmakers with facts (or states of affairs) — structured entities that bind objects and properties together. Armstrong's key insight was that the world is not just a collection of floating objects and properties. If we list the object Socrates and the property wisdom, that doesn't yet tell us whether Socrates is wise. What tells us is the fact: Socrates's being wise — a structured entity in which Socrates instantiates wisdom. This fact, if it exists, *necessitates* the truth of "Socrates is wise." The truthmaker necessitation principle holds that if a truthmaker exists, it cannot fail to make its proposition true. The proposition doesn't merely coexist with the truthmaker; the truthmaker's existence entails the proposition's truth.
The intuitive picture quickly generates puzzles. Consider negative truths: "there are no unicorns." What is the truthmaker for this? No particular unicorn exists to serve that role. No specific fact about existing things in isolation does it — any such fact could coexist with a unicorn somewhere else. Totality facts are one proposed solution: a special fact that what exists is *all* that exists — a "that's all" fact that precludes unicorns. But totality facts are ontologically costly: they seem to require a global fact over all particulars, which is hard to individuate and arguably more mysterious than what we started with. Universal generalizations ("all ravens are black") pose the same difficulty.
These puzzles motivate a debate about truthmaker maximalism — the view that every truth has a truthmaker — versus more modest positions that require truthmakers only for positive, particular truths. From your study of universals, you'll recognize how ontological options interact here: if we accept immanent universals (properties as constituents shared across instances), facts can have universals as constituents alongside particulars, giving a rich inventory for truthmakers. Nominalists, who reject universals, must construct truthmakers from particulars alone — tropes (particularized property instances, like *this* redness of *this* rose) are one option. Truthmaker theory thus functions as a unifying pressure on all of metaphysics: whatever ontology you endorse, it must generate truthmakers for all the truths you affirm.
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