Hallucinations: Detection, Grounding, and Abstention

A model trained to predict the next token has nothing in its objective that represents truth, so a fabricated citation is a plausible continuation rather than a malfunction. This cursus covers what follows: the taxonomy that tells you whether a failure is a generation or a corpus problem, why fluency carries no signal and why self-review does not work, grounding and the detection methods that compare output against something external, and abstention, including calibration, the coverage-accuracy trade, and building a system that can say it does not know.