# Hallucination

Canonical: https://aimastermindlab.com/glossary/hallucination

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Hallucination is when an AI language model generates plausible-sounding but factually incorrect or entirely fabricated information. The model 'hallucinates' facts, citations, names, or events that do not exist, presenting them with false confidence.

## What is AI Hallucination?

Hallucination refers to the phenomenon where a language model generates statements that are **convincingly written but factually wrong**. The model produces output that sounds authoritative, yet the information is either incorrect, distorted, or entirely invented.

## Types of Hallucination

- **Factual hallucination** — Stating incorrect facts ("The Eiffel Tower is in Rome").
- **Citation hallucination** — Fabricating papers, sources, or URLs that don't exist.
- **Entity hallucination** — Inventing people, companies, or products.
- **Reasoning hallucination** — Producing plausible but logically flawed reasoning chains.

## Why LLMs Hallucinate

LLMs are trained to predict the most statistically likely next token. They don't have a separate "fact-checking" module — they generate text that *fits the pattern* of a reasonable answer, regardless of whether it's true. When the model lacks relevant training data, it fills the gap with plausible-sounding fabrications.

## Mitigating Hallucinations

- **RAG** — Ground responses in retrieved factual documents.
- **Temperature reduction** — Lower temperature produces more deterministic, less creative outputs.
- **Constitutional AI / RLHF** — Train the model to prefer accurate, verifiable responses.
- **Tool use / grounding** — Give the model access to search, calculators, or databases.
- **Verification layers** — Post-process outputs to check claims against external sources.

## Example

Ask an LLM for citations for a niche academic topic, and it may confidently produce a list of paper titles, authors, and DOIs — none of which actually exist.
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Source: https://aimastermindlab.com/glossary/hallucination — AI Mastermind Lab (https://aimastermindlab.com)