Hallucination: Why AI Confidently Lies

A hallucination is when an AI makes something up — but states it as if it were certainly true.

What is it?

A hallucination is a false statement from an AI that still sounds confident and convincing. For example, the AI might invent a book, a law, or a function in a library that doesn't actually exist — and phrase it as plain fact.

Why does it happen?

An LLM predicts the most likely next word, one at a time (see LLM). It has no built-in "truth checkbox". If it doesn't actually know the real answer, it still fills the gap with plausible-sounding text — because sounding plausible is exactly what it was trained to do.

When does it happen most?

With very specific facts (names, numbers, quotes)
With questions about things after the training cutoff
With niche topics that had little training data
When asked about things that don't exist ("tell me about function X in library Y")

What helps against it?

Give the AI real sources or documents as context instead of letting it guess
Always double-check important facts, especially numbers, quotes, API names
Ask the AI to state uncertainty instead of guessing