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On Limitations of the Transformer Architecture

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arxiv 2402.08164 v2 pith:UFXXH6BV submitted 2024-02-13 stat.ML cs.AIcs.LG

classification stat.MLcs.AIcs.LG
keywords largecomplexitydomainsenoughfunctionsllmstaskstransformer
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What are the root causes of hallucinations in large language models (LLMs)? We use Communication Complexity to prove that the Transformer layer is incapable of composing functions (e.g., identify a grandparent of a person in a genealogy) if the domains of the functions are large enough; we show through examples that this inability is already empirically present when the domains are quite small. We also point out that several mathematical tasks that are at the core of the so-called compositional tasks thought to be hard for LLMs are unlikely to be solvable by Transformers, for large enough instances and assuming that certain well accepted conjectures in the field of Computational Complexity are true.

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Forward citations

Cited by 11 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Ehrenfeucht-Haussler Rank and Chain of Thought

    cs.LG 2025-01 conditional novelty 8.0 of 10

    A function's Ehrenfeucht-Haussler rank exactly equals the minimum chain-of-thought steps for a single-layer hard-attention Transformer, with matching lower bounds for iterated composition and the k-th-one function.

  2. Gadgetless Lifting Beats Round Elimination: Improved Lower Bounds for Pointer Chasing

    cs.CC 2024-11 conditional novelty 8.0 of 10

    The paper shows that any (k−1)-round protocol for the k-step pointer chasing problem requires Ω(n/k + k) communication, improving the previous Ω(n/k − k log n) bound.

  3. Attention-based representations for multi-task computation

    cs.LG 2026-08 accept novelty 7.0 of 10

    For min/max readout, two attention heads beat one head by an exponential resource gap, and for n-bit parity and symmetric Boolean functions, heads times polynomial degree must reach the threshold degree, with matching...

  4. When Does In-Context Search Help? A Sampling-Complexity Theory of Reflection-Driven Reasoning

    cs.AI 2026-07 conditional novelty 7.0 of 10

    When reflections localize early errors, in-context search solves exp-small pass-rate problems with poly sequential attempts; otherwise it offers no asymptotic gain over parallel sampling, and the update is learnable a...

  5. Provably Overwhelming Transformer Models with Designed Inputs

    cs.LG 2025-02 conditional novelty 7.0 of 10

    A verification algorithm proves that a trained single-layer transformer is 'overwhelmed' by a chosen prefix, meaning its output is insensitive to any appended string of bounded length.

  6. Lower bounds on transformers with infinite precision

    cs.LG 2024-12 conditional novelty 7.0 of 10

    One-layer infinite-precision softmax transformers need at least polynomial embedding dimension or output MLP size to compute function composition or SUM2.

  7. Quantum Coordination Advantages in AI State-Tracking Tasks: Semantic Compilation and Latent Memory

    quant-ph 2026-08 conditional novelty 6.0 of 10

    A boundary-preserving semantic-compilation theorem converts known one-way, streaming, and contextuality separations into architecture-independent coordination-width lower bounds for AI state-tracking solvers, with thr...

  8. (Im)possibility of Automated Hallucination Detection in Large Language Models

    cs.LG 2025-04 conditional novelty 6.0 of 10

    Automated hallucination detection is equivalent to identifying the true language from positive data: impossible for most countable collections without negative examples, and always possible with them.

  9. Linear Correlation in LM's Compositional Generalization and Hallucination

    cs.CL 2025-02 conditional novelty 6.0 of 10

    Language models' next-token predictions for related knowledge are connected by near-linear transformations that persist through fine-tuning, explaining both compositional generalization and hallucination.

  10. Constructing Set-Compositional and Negated Representations for First-Stage Ranking

    cs.IR 2025-01 conditional novelty 6.0 of 10

    Vector operations on learned sparse representations compose union, intersection, and negation queries without fine-tuning, and adding negative term weights to SPLADE improves negation handling.

  11. Pause Tokens Strictly Increase the Expressivity of Constant-Depth Transformers

    cs.LG 2025-05 reject novelty 5.0 of 10

    The paper claims pause tokens strictly increase constant-precision, constant-depth Transformer expressivity from a subset of AC0 to AC0 (and log-precision to TC0), but the constant-precision proof is not sound as written.

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