 The English discourse  (21)  is clearly consistent: it is nothing like saying I shirked my duty and I did not shirk my duty. This property of counterfactual antecedents is known by a technical name, non-monotonicity, and is one of the features all contemporary accounts are designed to capture. As will be discussed in  §2.2,  even modal logic does not have the resources to capture semantically non-monotonic operators.