Although the Modus Ponens inference is one of the most basic logical rules, decades of conditional reasoning research show that it is often rejected when people consider stored background knowledge about potential disabling conditions. In the present study we used EEG to identify neural markers of this process. We presented participants with many and few disabler conditionals for which retrieval of disabling conditions was likely or unlikely. As in classic behavioral studies we observed that participants accepted the standard MP conclusion less for conditionals with many disablers. The key finding was that the presentation of the standard MP conclusion also resulted in a more pronounced N2 and less pronounced P3b for the many disabler conditionals. This specific N2/P3b pattern has been linked to the violation and satisfaction of expectations, respectively. Thereby, the present ERP findings support the idea that disabler retrieval lowers reasoners' expectations that the standard MP conclusion can be drawn. (C) 2014 Elsevier Ltd. All rights reserved.