This paper presents a study investigating whether and how different kinds of knowledge affect the detection of plausibility and possibility violations. Readers' eye-movements were monitored while reading sentences describing impossible events cued by selectional restriction violations, extremely implausible events without selectional restriction violations, and plausible events, in order to determine whether the time course of disruption is determined by overall implausibility/unlikelihood, or whether impossibility cued by selectional restriction violations additionally affects disruption. Both early and late fixation measures showed stronger disruption in the impossible/selectional restriction violation condition. However, measures indexing regressive eye-movements showed similar disruption in both extremely implausible conditions. This suggests that the magnitude and latency of disruption to possibility and plausibility violations is not a simple function of the overall implausibility/unlikelihood of the resulting event, but that selectional restriction violations influence the early and late time course of disruption.