Finding: Models trained on MNLI, including BERT, perform poorly on HANS examples designed to expose lexical-overlap, subsequence and constituent heuristics.
Boundary: This diagnoses specific syntactic behavior in natural language inference. It does not show that every Transformer fails every task, or that BERT’s reported benchmark gains were false.
Research note: Add a targeted challenge set; a high aggregate score can hide a systematic failure mode.
Original source — Abstract; HANS evaluation · ACL 2019