The Grammar of Transformers: A Systematic Review of Interpretability Research on Syntactic Knowledge in Language Models

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Hauptverfasser: Graichen, Nora, de-Dios-Flores, Iria, Boleda, Gemma
Format: Preprint
Veröffentlicht: 2026
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author Graichen, Nora
de-Dios-Flores, Iria
Boleda, Gemma
author_facet Graichen, Nora
de-Dios-Flores, Iria
Boleda, Gemma
contents We present a systematic review of 337 articles evaluating the syntactic abilities of Transformer-based language models (TLMs), reporting on over 3,000 datapoints spanning a wide range of syntactic phenomena, languages, models, and methods. We take the data to collectively show that TLMs encode a non-trivial amount of syntactic knowledge. Behavioral evidence shows strong performance on formal syntactic phenomena, but weaker and more variable performance on phenomena at the syntax-semantics interface. Performance is also consistently lower for languages with less digital support. Probing and mechanistic studies further support the presence of syntactic knowledge in TLMs. Yet, because most work remains observational and current approaches are methodologically heterogeneous, insight into the detailed computational mechanisms underlying syntactic processing remains limited. At the same time, the literature remains heavily concentrated on English and BERT-like models. We discuss the implications of our results and provide recommendations for future research.
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id arxiv_https___arxiv_org_abs_2601_19926
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publishDate 2026
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spellingShingle The Grammar of Transformers: A Systematic Review of Interpretability Research on Syntactic Knowledge in Language Models
Graichen, Nora
de-Dios-Flores, Iria
Boleda, Gemma
Computation and Language
Artificial Intelligence
We present a systematic review of 337 articles evaluating the syntactic abilities of Transformer-based language models (TLMs), reporting on over 3,000 datapoints spanning a wide range of syntactic phenomena, languages, models, and methods. We take the data to collectively show that TLMs encode a non-trivial amount of syntactic knowledge. Behavioral evidence shows strong performance on formal syntactic phenomena, but weaker and more variable performance on phenomena at the syntax-semantics interface. Performance is also consistently lower for languages with less digital support. Probing and mechanistic studies further support the presence of syntactic knowledge in TLMs. Yet, because most work remains observational and current approaches are methodologically heterogeneous, insight into the detailed computational mechanisms underlying syntactic processing remains limited. At the same time, the literature remains heavily concentrated on English and BERT-like models. We discuss the implications of our results and provide recommendations for future research.
title The Grammar of Transformers: A Systematic Review of Interpretability Research on Syntactic Knowledge in Language Models
topic Computation and Language
Artificial Intelligence
url https://arxiv.org/abs/2601.19926