Philosophy
The Metaphysics of Causation: Counterfactual, Regularity, and Process Theories
Quick fact
David Lewis's counterfactual theory of causation defines a cause as an event that makes a difference: had the cause not occurred, the effect would not have occurred either, in the closest possible worlds. This elegantly handles many everyday causal claims but famously struggles with cases of causal overdetermination, where two independent causes are both sufficient for the effect.
Why this is interesting
We all think we know what causation is—a billiard ball hits another and it moves. But philosophers have found that 'cause' is surprisingly slippery: is it just a pattern, a counterfactual, or a physical process?