Whether people possess free will has been a long-lasting philosophical debate. Recent attention in social psychology has been given to the behavioral consequences of believing in free will. Research has demonstrated that manipulating free will beliefs has implications for many social behaviors. For example, free will belief manipulations have been associated with cheating, aggressiveness, and prejudice. Despite this work, some of these findings have failed to replicate. Testing theoretical predictions, such as whether believing in free will influences behavior, depends on theoretical, auxiliary, statistical, and inferential assumptions (TASI). In this paper we apply the TASI category of assumptions to the free will belief debate. In doing so we demonstrate why these assumptions should be considered when appraising the influence of free will belief manipulations on free will beliefs and behavior. To provide a nuanced view of free will beliefs, we believe researchers should pay careful attention to these critical assumptions.