Why Large Language Models Hallucinate

10 minutesNew to AIFoundationIBM TechnologyChatGPT & LLMs

IBM Technology. Martin Keen sorts hallucinations into four named buckets — sentence contradictions, prompt contradictions, factual errors, nonsense — and walks through each on a lightboard. After the article gives you the why, this video gives you a vocabulary for spotting the type of mistake in the wild so you can decide how much to trust a given answer.

AI Expert note

Chosen for the four-bucket vocabulary rather than depth; read the article first so the taxonomy has the why underneath it.

What you should get from this

You can name the four kinds of hallucination and recognize which one you are looking at when a chatbot gets something wrong.

Watch or know first

None — watchable cold.

Last reviewed: May 18, 2026

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