arXiv cs.CL
7/1/2026

When transformers learn "impossible" languages, what do they learn?
Short summary
Transformers trained on linguistically "impossible" languages show gradual degradation in grammatical sensitivity but pronounced failures in longer-form generation. Using BLiMP minimal pairs to separate capacities, researchers found generative deficiency—not grammatical insensitivity—drives model behavior. This explains why certain language structures don't exist in human languages: they violate production constraints.
- •Models degrade gradually on grammatical sensitivity for unnatural languages
- •Severe failures appear in generation, not in detecting grammaticality
- •Generative constraints, not grammatical ones, explain why certain structures don't exist in nature
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