© The Author(s) 2019. The core idea of truth-default theory (T. R. Levine, 2014) is that when people cognitively process the content of others' communication, they typically do so in a manner characterized by unquestioned, passive acceptance. Two deception detection experiments tested the existence of the truth-default by comparing prompted and unprompted evaluations of others. The first experiment involved viewing videotaped communication, and the second experiment involved live, face-to-face interactions. In both experiments, research confederates told the truth and lied about plausible and implausible autobiographical content. Participants completed both traditional, prompted, dichotomous truth-lie assessments and open-ended thought-listing measures. The order of the two types of measures was experimentally varied. The results supported the concept of a truth-default. Coded thought listings showed that, absent prior prompting, receivers mentioned consideration of the veracity of other's communication less than 10% of the time.