Plain-English AI definitions for legal professionals. For what bars actually require, see the Legal AI Compliance Register.
legalai.help

Hallucination

Using AI Last reviewed 2026-06-11

Definition An AI model's confident production of false information—invented facts, quotes, or citations—presented as though true. A structural byproduct of how language models generate text by probability rather than by looking facts up.

In more depth

Because a language model composes each answer token by token from learned patterns, it can produce output that is fluent, specific, and wrong—including case citations that do not exist. Hallucination can be reduced through retrieval-augmented generation and careful prompting, but it has not been eliminated in any current system. Fabricated citations in court filings have led to sanctions against lawyers, and bar authorities generally treat verification of AI output as part of the duty of competence.

Further reading: Wikipedia.

Related terms

Large language model (LLM)Retrieval-augmented generation (RAG)Human in the loop (HITL)

About the editor: MHSB Solutions, Research desk. MHSB Solutions is not a law firm. This glossary is educational information, not legal advice.

Educational information, not legal advice. AI terminology and tools change quickly; definitions reflect usage as of the last-updated date. For what bar associations and courts actually require of lawyers using AI, see legalaicompliance.help and consult a licensed attorney in your jurisdiction.