 Reichenbach argues that spatially and temporally close coincidences of two causal processes suffice to determine that the coincidence is either a common cause or a common effect of two other events. (He postpones the issue of how it can be known that there is any causal connection between remote events.) He claims, correctly, that this implies that a causally connected network—an acyclic directed graph—of events can have only two orientations; reversing any edge requires reversing all other edges to yield an equivalent directed graph. In an anticipation of 21st century discussions (Woodward, 2003), he considers whether interventions can disambiguate cause from effect in such a network, and argues that they cannot, on counterfactual considerations that are not entirely clear to us. 