 the probability that E occurs, given that C occurs, is higher than the probability that E occurs, given that C does not occur. These two formulations turn out to be equivalent in the sense that inequality \(\PR_1\) will hold just in case \(\PR_2\) holds. Some authors (e.g., Reichenbach 1956, Suppes 1970, Cartwright 1979) have formulated probabilistic theories of causation using inequalities like \(\PR_1\), others (e.g., Skyrms 1980, Eells 1991) have used inequalities like \(\PR_2\). This difference is mostly immaterial, but for consistency we will stick with (\(\PR_2)\). Thus a first stab at a probabilistic theory of causation would be: