Truth-default theory (TDT) is a communication theory which predicts and explains the use of veracity and deception detection in humans. It was developed upon the discovery of the veracity effect - whereby the proportion of truths versus lies presented in a judgement study on deception will drive accuracy rates. This theory gets its name from its central idea which is the truth-default state. This idea suggests that people presume others to be honest because they either don't think of deception as a possibility during communicating or because there is insufficient evidence that they are being deceived. Emotions, arousal, strategic self-presentation, and cognitive effort are nonverbal behaviors that one might find in deception detection. Ultimately this theory predicts that speakers and listeners will default to use the truth to achieve their communicative goals. However, if the truth presents a problem, then deception will surface as a viable option for goal attainment.