incoherent

Incoherent is an adjective meaning lacking coherence: not logically connected, lacking clarity or consistency, or not forming a unified whole. It is commonly used to describe speech, writing, or arguments that are difficult to understand or follow.

In discourse and communication, incoherence refers to a breakdown in cohesion: failure to maintain a topic, abrupt shifts, or missing transitions. It can arise from confusion, hurried speech, or cognitive impairment. In clinical contexts, incoherent speech may signal delirium, dementia, mania, or intoxication.

In physics and optics, incoherent describes waves that lack a fixed phase relationship. Incoherent light consists of many photons with random phases, as opposed to coherent light from a laser, which has a stable phase relation. The term also appears in statistics when signals are combined without phase alignment, producing no consistent interference pattern.

Etymology and related terms: incoherent comes from Latin incohaerent-, from in- “not” + cohaerere “to cling together.” Related concepts include coherence and coherent, which denote logical unity and constructive phase relationships, respectively. The term is widely used across disciplines to indicate absence of a stable, unified, or interpretable structure.