 [O]ne supposes the antecedent and develops the supposition, adding further judgments within the supposition by reasoning, offline predictive mechanisms, and other offline judgments. The imagining may but need not be perceptual imagining. All of one’s background beliefs are available from within the scope of the supposition as a description of one’s actual circumstances for the purposes of comparison with the counterfactual circumstances… Some but not all of one’s background knowledge and beliefs are also available within the scope of the supposition as a description of the counterfactual circumstances, according to complex criteria… To a first approximation: one asserts the counterfactual conditional if and only if the development [of the antecedent] eventually leads one to add the consequent. (2007: 152–153)