Deception refers to the act—big or small, cruel or kind, casual or calculated—of causing someone to believe something that is untrue. Even the most honest among us practice deception, with various studies showing that the average person lies several times a day. Some of those lies are big (“Of course I’ve never cheated on you!”) but more often, they are little white lies (“Yes, that dress looks fine,”) that are deployed to avoid uncomfortable situations or spare the feelings of a person we care about. Some kinds of deception aren’t exactly lies—like combing hair over a bald spot or nodding when you’re not really listening.
Deception isn’t always an outward-facing act. There are also the lies we tell ourselves, for reasons ranging from healthy maintenance of self-esteem to serious delusions beyond our control. While lying to yourself is generally perceived as harmful, some experts argue that there are certain kinds of self-deception—believing you can achieve a difficult goal, for instance, even if evidence exists to the contrary—that can have a positive effect on your wellbeing and lead to improved problem-solving capabilities.
Since the early 20th century, researchers have searched for ways to definitively detect when someone is lying. One of the most well-known, the polygraph test, measures physiological responses—including blood pressure and skin conductivity—thought to change when someone is telling a lie. Polygraphs have long been controversial, and evidence suggests that those with certain psychiatric disorders—like Antisocial Personality Disorder or schizophrenia—cannot be accurately measured by polygraphs or other commonly-used lie detection methods. In 2003, the National Academy of Sciences reviewed polygraph-related research, concluding that while the overall evidence for polygraphs was “scanty and scientifically weak,” when used appropriately on someone “untrained in countermeasures,” the tool could “discriminate lying from truth telling at rates well above chance—though well below perfection.”