Source amnesia is the inability to remember where, when, or how information was acquired, even though the information itself is retained. The content is available; the origin is lost.

A person may know a fact yet misattribute it to a newspaper rather than to a conversation, or may believe an imagined event actually occurred. Source amnesia contributes to false memories and to the sleeper effect, in which a message from a low-credibility source becomes more persuasive over time as the source is forgotten. Older adults are particularly prone to source confusions.

The phenomenon reveals that memory for content and memory for context are supported by partially distinct processes. The hippocampus and prefrontal regions are implicated in binding and later retrieving source information. When that binding fails, the fact floats free of its origin and can be reassembled incorrectly.

Knowing something without knowing how one knows it is the everyday face of source amnesia.