---
title: "Don't Say That! Making Inconsistent Dialogue Unlikely with"
description: "Generative dialogue models trained only with maximum likelihood show several weaknesses. 28 references, cited by 91 papers here."
authors: ["Margaret Li", "Stephen Roller", "Ilia Kulikov", "Sean Welleck", "Y-Lan Boureau", "Kyunghyun Cho", "Jason Weston"]
year: 2020
venue: "Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics"
source: "https://aclanthology.org/2020.acl-main.428/"
doi: "10.18653/v1/2020.acl-main.428"
licence: "CC BY 4.0 (ACL Anthology)"
licence_url: "https://creativecommons.org/licenses/by/4.0/"
summary_licence: "Elamur Cosmic License"
canonical: "https://research.elamur.ai/free/en/papers/li-2020-don-t-say-that-making/"
---
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# Don't Say That! Making Inconsistent Dialogue Unlikely with Unlikelihood Training

**Authors:** [Margaret Li](https://md.research.elamur.ai/free/en/authors/margaret-li/), [Stephen Roller](https://md.research.elamur.ai/free/en/authors/stephen-roller/), [Ilia Kulikov](https://md.research.elamur.ai/free/en/authors/ilia-kulikov/), [Sean Welleck](https://md.research.elamur.ai/free/en/authors/sean-welleck/), [Y-Lan Boureau](https://md.research.elamur.ai/free/en/authors/y-lan-boureau/), [Kyunghyun Cho](https://md.research.elamur.ai/free/en/authors/kyunghyun-cho/) and [Jason Weston](https://md.research.elamur.ai/free/en/authors/jason-weston/) · **Year:** 2020 · **Venue:** [Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics](https://md.research.elamur.ai/free/en/venues/acl/) ([ACL 2020](https://md.research.elamur.ai/free/en/venues/acl/2020/)) · **Publisher:** [Association for Computational Linguistics](https://md.research.elamur.ai/free/en/publishers/association-for-computational-linguistics/) · **Licence:** [CC BY 4.0 (ACL Anthology)](https://creativecommons.org/licenses/by/4.0/)

**Links:** [Publisher's page](https://aclanthology.org/2020.acl-main.428/) · [PDF](https://aclanthology.org/2020.acl-main.428.pdf) · [DOI 10.18653/v1/2020.acl-main.428](https://doi.org/10.18653/v1/2020.acl-main.428) · [OpenAlex](https://openalex.org/W3035068109)

**Citations:** 124 citations (OpenAlex, 2026-10-14) · [91](https://md.research.elamur.ai/free/en/papers/li-2020-don-t-say-that-making/cited-by/) in our library, of the 141,840 papers whose bibliographies we read

## Summary

Generative dialogue models trained only with maximum likelihood show several weaknesses. They copy too much from the context, repeat n-grams inside a single reply, overuse frequent tokens, and can contradict what was said earlier. The authors extend the unlikelihood loss of Welleck et al. (2019a) into a general framework. Alongside standard likelihood, it adds a term that lowers the probability of chosen "negative candidate" tokens. Different choices of candidates and per-token weights target different flaws:

- n-grams copied from the context or repeated within the generated reply,
- tokens the model produces more often than humans, weighted by the gap between the model's and the human unigram distributions,
- whole contradictory responses built from Dialogue NLI labels.

All experiments fine-tune a seq2seq Transformer pre-trained on pushshift.io Reddit. The statistical penalties move generated text closer to human statistics. The NLI-based training teaches the model to assign much lower probability to contradictions, while overall perplexity on ConvAI2 barely changes. This matters because it shows that labeled data about unwanted behavior can be built directly into generator training, rather than only used to rescore outputs.

## Key points

- Base model: a Transformer with an 8-layer encoder and an 8-layer decoder, 512-dimensional embeddings and 16 attention heads, built in ParlAI. It was pre-trained on roughly 2200M pushshift.io Reddit examples.
- The MLE baseline reaches a perplexity of 11.4 on ConvAI2, and unlikelihood training raises it only slightly, to about 11.8–11.9.
- On the Dialogue NLI two-utterance task, the baseline assigns lower perplexity to contradictions (12.5) than to neutral (36.7) or triple-entailing (17.5) replies. After unlikelihood training, contradiction perplexity rises to 248.9, compared with 9.1 for entailing replies.
- On the same task, selection accuracy for neutral over contradicting replies grows from 18% to 78%, and for entailing replies from 72% to 96%.
- On the full-dialogue variant, neutral selection accuracy rises to 69.8% from about 37%. Code and models are released via parl.ai (dialogue_unlikelihood project).

*Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.*

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## Cite

Cite as: Margaret Li, Stephen Roller, Ilia Kulikov, Sean Welleck, Y-Lan Boureau, Kyunghyun Cho and Jason Weston. 2020. Don't Say That! Making Inconsistent Dialogue Unlikely with Unlikelihood Training. Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics.

The paper itself, not this page. BibTeX from the library's record of the work.

```bibtex
@inproceedings{li2020don,
  title = {{Don't Say That! Making Inconsistent Dialogue Unlikely with Unlikelihood Training}},
  author = {Margaret Li, Stephen Roller, Ilia Kulikov, Sean Welleck, Y-Lan Boureau, Kyunghyun Cho and Jason Weston},
  booktitle = {Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics},
  year = {2020},
  doi = {10.18653/v1/2020.acl-main.428},
  url = {https://doi.org/10.18653/v1/2020.acl-main.428}
}
```

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28. Token frequency classes Model PPL F1 Context Label -- .400 .300 11.4 .199 .491 .282 F1 Freq Med Rare Rarest .200 .157 .100 .068 Human MLE Baseline -- 8.3 .373 .160 .0006 .582 .002 UL (Context only) UL (Label only) UL (Context + Label) 8.8 .345 8.3 .371 8.5 .358 .270 .645 .445 Nucleus p = 0.3 Nucleus… [find](https://scholar.google.com/scholar?q=Token+frequency+classes+Model+PPL+F1+Context+Label+%2D%2D+%2E400+%2E300+11%2E4+%2E199+%2E491+%2E282+F1+Freq+Med+Rare+Rarest+%2E200+%2E157+%2E100+%2E068+Human+MLE+Baseline+%2D%2D+8%2E3+%2E373+%2E160+%2E0006+%2E582+%2E002+UL+%28Context+only%29+UL)

*Updated 24 October 2026*