Paraphrasing as Zero-shot Translation with Feature-guided Diversity Enhancement
Summary
Training paraphrasers on parabanks built by machine-translating one side of a parallel corpus has two weaknesses. The MT system has usually seen that same corpus, so its outputs stay close to the references and lack variety. The paraphraser also learns only from the derived parabank, which holds just part of the knowledge in the original data. The authors propose ParaMNMT, a single-stage alternative. They train a bidirectional multilingual NMT model on English-Czech WMT 2016 data, with target-language tokens prepended to each sentence. To paraphrase, they ask the model for a zero-shot "translation" into the input's own language. To counter outputs that simply echo the input, each source token gets a "copy" or "not-copy" feature embedding during training, marking whether it reappears in the target. At inference, labelling more tokens "not-copy" pushes the model to rewrite them. In manual and automatic evaluation, the resulting paraphrases beat existing parabanks and LLMs on meaning preservation, fluency and diversity. As augmentation data, they improve low-resource GLUE tasks and low-resource MT, which matters for low-resource NLP settings.
Key points
- Training data and model:
- Data: the WMT 2016 English-Czech corpus (Europarl v7, Common Crawl, News Commentary v11, CzEng 1.6pre), reversed to cover both directions, with shared BPE.
- Model: Transformer Base (6 layers, 512-dimensional embeddings) with LALN and LALT.
- Copy tags: In the training data, 18.7% of source tokens carry the "copy" tag. At inference, 30% of tokens are tagged "not-copy." Two ways of choosing them were compared: by high frequency, or by high BERT-based entropy.
- Tag compliance: The model disregards a "not-copy" instruction in about 7.17% of cases.
- GLUE gains: Augmentation helps even on top of a LoRA-tuned Qwen 3 8B baseline, for example CoLA 63.4→65.5, SST-2 95.6→97.6 and MNLI 90.9→92.4.
- Translation gains: BLEU with Qwen 3 8B rises from prompting to LoRA to LoRA plus ParaMNMT:
- En-De: 27.27 → 30.49 → 31.30
- En-Tr: 20.03 → 22.61 → 23.54
- En-Fi: 17.58 → 18.95 → 19.63
Cite
@inproceedings{yan2026paraphrasing,
title = {{Paraphrasing as Zero-shot Translation with Feature-guided Diversity Enhancement}},
author = {Yan, Ziyue and Zan, Hongying and Lyu, Xinglin and Xu, Hongfei},
booktitle = {Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)},
year = {2026},
doi = {10.18653/v1/2026.acl-long.783},
url = {https://doi.org/10.18653/v1/2026.acl-long.783}
}References
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