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This paper introduces SAE-IDF, a novel data-driven approach for aligning symbolic representations across heterogeneous systems by leveraging sparse autoencoders (SAEs) to encode symbols into interpretable sparse codes. By re-weighting these sparse dimensions based on their rarity, SAE-IDF achieves superior symbolic matching performance compared to dense baselines on diverse tasks and LLMs. The interpretability of SAE dimensions allows for human-understandable decomposition of matches into named concepts, paving the way for scalable, universal symbolic backbones.
Sparse autoencoders unlock a shared, interpretable coordinate system for matching symbols across diverse AI systems, outperforming dense baselines by up to 45 points.
Large language models (LLMs) hold broad knowledge in one set of weights, but lack interpretability and trustworthy reasoning, especially in high-stakes use cases. A neuro-symbolic model, with its interpretable architecture and System 2 reasoning capacity, is a promising alternative if built at the scale of LLMs; however, its symbolic backbone is usually constructed with human effort, so existing neuro-symbolic models are bottlenecked by the scope of the symbol component and usually domain-specific. A data-driven method could instead build a larger symbolic system by aligning and merging existing ones. We target its first, foundational step: matching units across these heterogeneous systems. Our method, SAE-IDF, encodes a symbol in its native context into a sparse code with a sparse autoencoder (SAE), re-weights each dimension by its rarity and matches across systems. On 12 tasks across 6 kinds of symbolic system, SAE-IDF outperforms the same LLM's dense baseline on all tasks with Gemma-2-9B and all but one with Llama-3.1-8B, by up to 45 points, consistently across SAE layers and configurations. SAE-IDF is also interpretable: every dimension of the sparse code has a human-readable meaning, so each match decomposes into named concepts (features). Our work paves the way to a universal symbolic backbone.