 How does X evaluate “If \(A, B\)”? She assumes that \(A\), that is, hypothetically eliminates \({\sim}A\). In the part of the partition that remains, in which \(A\) is true, \(B\) is four times as likely as \({\sim}B\); that is, on the assumption that \(A\), it is four to one that \(B: \mathbf{p}(B\) if \(A)\) is 80%, \(\mathbf{p}({\sim}B\) if \(A)\) is 20%. Equivalently, as \(A \amp B\) is four times as likely as \(A \amp{\sim}B, \mathbf{p}(B\) if \(A)\) is 4/5, or 80%. Equivalently, \(\mathbf{p}(A \amp B)\) is 4/5 of \(\mathbf{p}(A)\). In non-numerical terms: you believe that if \(A, B\) to the extent that you think that \(A \amp B\) is nearly as likely as \(A\); or, to the extent that you think \(A \amp B\) is much more likely than \(A \amp{\sim}B\). If you think \(A \amp B\) is as likely as \(A\), you are certain that if \(A, B\). In this case, your \(\mathbf{p}(A \amp{\sim}B) = 0\).