 If X is a variable in a causal model, and x is a particular value in the range of X, then \(X = x\) is an atomic proposition. The logical operations of negation (“not”), conjunction (“and”), disjunction (“or”), the material conditional (“if…then…”), and the biconditional (“if and only if”) are represented by “\({\sim}\)”, “&amp;”, “\(\lor\)”, “\(\supset\)”, and “\(\equiv\)” respectively. Any proposition built out of atomic propositions and these logical operators will be called a Boolean proposition. Note that when the variables are defined over individuals in a population, reference to an individual is not included in a proposition; rather, the proposition as a whole is true or false of the various individuals in the population.