 Thus Reichenbach seems to think that in II above, A and B are independent conditional on C, but in III, A and B are dependent conditional on C and the absence of D. Reichenbach’s confusions on these points is understandable—well into the 1990s much the same could be heard from several statisticians. In order to see the correct relations, Reichenbach would have had to have explicitly formulated the factorization of the joint distribution for binary variables that is implicit in his other discussions, and computed the joint distribution of independent causes conditional on values of a common effect. He did not. Alternatively, with linear systems it is trivial to calculate the partial correlations of the causes controlling for the effect, but Reichenbach undoubtedly did not know the formulas. 