This study employs the first systematic, empirical analysis that relies on archival data to examine whether the separation of powers influences justices' agenda votes. It spatially models how justices set the Court's agenda under a sincere approach as well as an SOP approach and compares the competing expectations derived therefrom. The results suggest that legislative and executive preferences fail to influence justices' votes. Across every model tested, the data show justices uninfluenced by the separation of powers. These results provide a strong rejoinder to SOP models, since the Court's agenda stage is the most likely stage of the decision-making process to show signs of an SOP effect.