types of hallucination

Not all hallucinations look the same, and sorting them helps you catch them. Factual hallucinations contradict the real world: a wrong date, a misattributed quote, a chemical that does not exist. Contextual or faithfulness hallucinations contradict the text you provided: you paste a document, ask for a summary, and the summary adds claims the document never made. Citation hallucinations invent sources — papers, authors, page numbers — that were never written.

A useful split is intrinsic versus extrinsic. Intrinsic hallucinations conflict with the input right in front of the model, so they are checkable by re-reading the source. Extrinsic hallucinations go beyond the input into outside knowledge, where checking means consulting the wider world. Knowing which kind you are facing tells you where to look to verify: back at the prompt, or out in reality.