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Are counterfactuals with true antecedents and consequents trivially true? The principle of Conjunction Conditionalization ((A∧C)→(A>C)) is highly controversial. Many philosophers view it as an attractive feature of Lewis's semantics for counterfactuals that it can easily be modified to avoid this principle. However, Walters and Williams (2013) beg to differ. They argue that Conjunction Conditionalization is an indispensable ingredient of any Lewisian semantics, since CC is entailed by standard Lewisian theorems and a plausible semantic claim about irrelevant semifactuals. If this is true, the entire tradition of revisionist counterfactual semantics is misguided, and so are many philosophical theories in which counterfactuals play a role. We argue, in defense of the revisionist tradition, that Walters and Williams' ‘plausible semantic claim’ is in fact anything but plausible. It turns out to entail semantic principles far more controversial than Conjunction Conditionalization.

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Response-dependence theses are usually formulated in terms of a priori true biconditionals of roughly the form 'something, x, falls under the concept 'F' $ x would elicit response R from subjects S under conditions C'. Such formulations are vulnerable to conditional fallacy problems; counterexamples threaten whenever the C-conditions' coming to obtain might alter the object with respect to F. Crispin Wright has suggested that such problems can be avoided by placing the C-conditions in a proviso. This ensures that any changes triggered by the C-conditions' coming to obtain will be irrelevant to the truth of the biconditional. I argue that this move leaves the equations vulnerable to counterexamples of a slightly different kind: Cases where the change is triggered, not by the C-conditions' coming to obtain, but by the response. I consider two ways to resist these counterexamples, and argue that both are insufficient. The upshot is a challenge that must be met if provisoed biconditionals are to serve their purpose.