 Note the restriction of \(t''\) to times earlier than or simultaneously with the occurrence of \(C_t\). That is because causal intermediates between \(C_t\) and \(E_{t'}\) will often screen \(C_t\) off from \(E_{t'}\). In such cases we still want to say that \(C_t\) is a cause of \(E_{t'}\), albeit a distal or indirect cause.