 (1) Suppose I believe \(p\) and \(p \supset q\) (as well as Modus Ponens). The mere fact that I have these beliefs and that I recognize them to jointly entail \(q\) does not normatively compel any particular attitude towards \(q\) on my part. In particular, it is not the case in general that I ought to come to believe \(q\) as  IMP  would have it. After all, \(q\) may be at odds with my evidence in which case it may be unreasonable for me to slavishly follow Modus Ponens and to form a belief in \(q\). The rational course of “action”, rather, when \(q\) is untenable, is for me to relinquish my belief in at least one of my antecedent beliefs \(p\) and \(p \supset q\) on account of their unpalatable implications. Thus, logical principles do not invariably offer reliable guidance in deciding what to believe (at least, when the relation between logical principles and our practices of belief-formation are understood along the lines of  IMP).  Let us therefore call this the Objection from Belief Revision.