Causation, as any other element of an actionable tort, has to be proven in the proceedings. As pointed out in Chapter 1, the causal link is not a fact; it is indeed a connection between two known facts, also defined as 'an empirical relation between concrete conditions'. It follows that it is not subject to the same burden of proof as any other evidence submitted to the court. The causal link needs a demonstration through logic, statistics and common sense, which is supported by general scientific theories and, simultaneously, by specific justification of the singular causation. Proof of singular causation therefore needs (1) scientific validity of causal generalizations that control the condition and (2) complete instantiation of the empirical relation.