 According to Jackson, in asserting “If \(A, B\)” the speaker expresses his belief that \(A \supset B\), and also indicates that this belief is “robust” with respect to the antecedent \(A\). In Jackson’s early work (1979, 1980) “robustness” was explained thus: the speaker would not abandon his belief that \(A \supset B\) if he were to learn that \(A\). This, it was claimed, amounted to the speaker’s having a high probability for \(A \supset B\) given \(A\), i.e. for \(({\sim}A\) or \(B)\) given \(A\), which is just to have a high probability for \(B\) given \(A\). Thus, assertability goes by conditional probability. Robustness was meant to ensure that an assertable conditional is fit for modus ponens. Robustness is not satisfied if you believe \(A \supset B\) solely on the grounds that \({\sim}A\). Then, if you discover that \(A\), you will abandon your belief in \(A \supset B\) rather than conclude that \(B\).