We study linguistic changes that failed, and their relation to successful changes. The inclusion of failed changes into Kroch&#8217;s logistic model of linguistic change is possible and, in fact, necessary. The logistic functions are solutions of a differential equation that also describes how failed changes are temporal-dynamically related to successful changes: the failed change is the first derivative of the successful change. We interpret this relation in Weerman&#8217;s Peripheral Rules Model: failed changes are L2 innovations supported by peripheral rules rather than by core grammar, which are subsequently accommodated and modified by L1 adopters and turned into a successful change. Two case studies support the claims: the rise of the reflexive in Dutch and the rise of <i>do</i>-support in English.