illusory

Illusory is an adjective used to describe something that appears real or true but is in fact deceptive or mistaken. It characterizes perceptions, beliefs, or outcomes that mislead by resembling reality while lacking substance. The term is commonly applied to visual or perceptual phenomena (illusory contours, optical illusions) as well as to cognitive biases and expectations (illusory correlations, illusory control).

Etymology and scope help clarify its use. Illusory derives from Latin illusorius, from illusio “an illusion” and illudere “to mock, deceive.” In English it has been used since the early modern period to indicate something that deceives by appearance rather than by intrinsic truth.

In psychology and related fields, illusory phenomena describe errors in interpretation where people infer connections, agency, or control that do not exist. Examples include illusory correlation, where two events seem related more often than chance would predict, and illusory control, the belief that one can influence random outcomes. The term is also used more broadly in everyday language to describe hopeful but unfounded or unfoundedly optimistic expectations or beliefs.

Distinctions are sometimes drawn between illusory and delusory. Illusory generally refers to appearances or beliefs that are mistaken or deceptive but not necessarily held in defiance of evidence, whereas delusory more often describes a belief maintained despite clear and persistent contrary evidence.