Concept · hallucination

Hallucination

Confidently produced output that is fluent but factually wrong or fabricated.

◷ Share view, as of June 2026: confidence, rationales and priors are hidden. The questions, stances, claims, tests and evidence stay visible.

Settled

Broad technical consensus on what this term means. Disagreements that invoke it are about the world, not the word.

What it is

A language model generates plausible next tokens; it does not consult a store of verified facts. Fabrication, invented citations, confident wrong answers, plausible nonexistent details, is therefore a failure mode of normal operation, not a malfunction. The fluency is the trap: errors arrive in the same confident voice as truths.

The term itself draws criticism (some prefer "confabulation"; some argue it anthropomorphizes), but the phenomenon it names is well established. It sits at the center of the reliability question: how much human oversight can be removed from a system that can fabricate?

Understand first

foundation-modelFoundation model · A single large pre-trained model that serves as a general-purpose base for many downstream uses.inferenceInference · Running a trained model to produce output: the 'using it' phase, as opposed to training.