 Under certain plausible assumptions an initial independence or initial randomness assumption allows us to derive a principle of the common cause (first proposed by Hans Reichenbach (1956)), according to which spatially distant correlated events A and B that are not related as cause and effect possess a common cause in their past that explains the correlation and screens off the correlation between A and B (Arntzenius 1999 [2010]). That is, formally, if