 We employ a notational convention where statements involving variables are understood to involve universal quantification over values of those variables (or over measurable sets of values). This version of the Causal Markov Condition says that the parents of variable X screen X off from all other variables, except for X itself and the descendants of X. Given the values of the variables that are parents of X, the values of the variables in \(\mathbf{Y}\) make no further difference to the probability that X will take on any given value. This version of the Causal Markov Condition is closest in form to Reichenbach’s Common Cause Principle, although it is formulated in terms of the parents of X, rather than the common cause(s) of X and Y.