Several philosophers have embraced the view that high-level events—events like Zimbabwe's monetary policy and its hyper-inflation—are causally related if their corresponding low-level, fundamental physical events are causally related. I dub the view which denies this without denying that high-level events are ever causally related causal emergentism. Several extant philosophical theories of causality entail causal emergentism, while others are inconsistent with the thesis. I illustrate this with David Lewis's two theories of causation (1973, 2000), one of which entails causal emergentism, the other of which entails its negation. I then argue for causal emergentism on the grounds that it provides the only adequate means of squaring the apparent plenitude of causal relations between low-level events with the apparent scarcity of causal relations between high-level events. This tension between the apparent abundance of low-level causation and the apparent scarcity of high-level causation has been noted before. However, it has been thought that various theses about the semantics or the pragmatics of causal claims could be used to ameliorate the tension without going in for causal emergentism. I argue that none of the suggested semantic or pragmatic strategies meet with success, and recommend emergentist theories of causality in their stead. As Lewis's 1973 account illustrates, causal emergentism is consistent with the thesis that all facts reduce to microphysical facts.

We sometimes say things like this: “being an animal is part of being a dog.” We associate the part with a precondition for exemplifying the whole. A new semantics for modal logic results when we take this way of speaking seriously. We need not treat necessary truths as truths in all possible worlds. Instead, we may treat them as preconditions for the existence of any world at all. I present this semantics for modal propositional logic and argue that it operates on a more basic level of modal reality than possible world semantics.