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.

The previous chapter has presented the general proof rules of causation in competition damages actions. These standard rules burden the claimant with the proof of the essential elements of a tort, including causation. However, the claimant may find it very difficult if not impossible to prove causation, especially when information is limited or is not accessible. As observed in Chapter 5, the standard proof rules place the risk for the proof of the claim and the risk of error due to evidential uncertainty on the claimant. The rules allocating this risk are mainly the result of policy-based decisions aiming at distributing the risk fairly between the parties based on a moral statement. However, on the basis of equally justifiable policy and moral choices, it is possible to create exceptions to this rule in two cases: (1) when the information is readily available to the other party and (2) when it is fair, according to the type of responsibility, to allocate the risk differently.