Many recent decisions in tort law attempt to combine two conceptually incommensurable features: a traditional 'but for' test of factual causation, and the scientific or medical evidence that is required to explain how some injury occurred. Even when applied to macroscopic objects, the 'but for' test fails to identify causes, because it merely rephrases in the language of possible worlds what may be inferred from what is inductively known about the actual world. Since scientific theories explain the occurrence of events (...) without reference to causes, this test of causation is not only ineffectual but also inapplicable to scientific or medical evidence. Tort law, therefore, should abandon the 'but for' test; when scientific or medical evidence is required in a tort case, the courts should rely on the explanatory strategies that function within the theories from which they borrow such evidence. (shrink)