{
  "id": "reversal-curse",
  "code": "PTL-0171",
  "term": "Reversal Curse",
  "aliases": [],
  "category": "failure-modes",
  "definition": "The reversal curse is the failure of language models trained on a fact stated as \"A is B\" to answer the reversed question \"what is B?\", for example knowing who a celebrity's mother is but not who that woman's famous son is.",
  "description": "It shows that models do not automatically store facts in both directions. In practice, providing the relevant fact in the prompt fixes it, since in-context reasoning handles the reversal, which is one more argument for retrieval over relying on memorized knowledge.",
  "example": null,
  "broader": [],
  "narrower": [],
  "related": [
    "hallucination",
    "knowledge-cutoff",
    "retrieval-augmented-generation"
  ],
  "introduced": 2023,
  "added": "2026-10-10",
  "sources": [
    {
      "title": "The Reversal Curse: LLMs trained on \"A is B\" fail to learn \"B is A\"",
      "authors": "Berglund et al.",
      "year": 2023,
      "url": "https://arxiv.org/abs/2309.12288"
    }
  ],
  "url": "https://protologue.com/t/reversal-curse/",
  "citation": "Protologue. (2026). Reversal Curse. In Protologue: A Taxonomy of Prompting and LLM Techniques (v1.4.0, PTL-0171). https://protologue.com/t/reversal-curse/"
}