Causal inference lies at the heart of many legal questions. Yet in the context of complicated disease litigation, in particular, the causal inquiry is beset with difficulties due to gaps in scientific knowledge concerning the precise biological processes underlying such diseases. Civil courts across the globe, faced with increased litigation on such matters, struggle to adhere to their judicial fact-finding and decision-making role in the face of such scientific uncertainty. An important difficulty in drawing evidentially sound causal inferences is the binary format of the traditional legal test for factual causation, being the but for test, which is based on the condicio-sine-qua-non principle. To the question would the damage have occurred in the absence of the defendant's wrongful behaviour the but for test requires a simple yes or no answer. This is increasingly deemed unsatisfactory in cases in which, given the state of science, true causation cannot possibly be determined with certainty.