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Can models be smart without organized internal structure?

Explores whether linear feature decodability proves genuine compositional reasoning or merely indicates that the right features are present but poorly organized. Critical for understanding what performance metrics actually certify.

Synthesis note · 2026-02-23 · sourced from MechInterp
What actually happens inside the minds of language models?

Two findings from mechanistic interpretability appear contradictory but operate at different levels of representational analysis:

Fractured Entangled Representations (FER): Since Can identical outputs hide broken internal representations?, SGD-trained models fail catastrophically under perturbation or distribution shift in ways that well-organized representations would not. The pathology is invisible to standard evaluation.

Compositional generalization at scale: Scaling data and model size produces representations where compositional features are linearly decodable — separable task constituents can be independently identified and manipulated. This has been taken as evidence for genuine compositional understanding.

The resolution: Linear decodability tests for the presence of features, not their organization. A fractured representation could contain every linearly decodable feature while being fractured in how those features relate to each other. The compositional parts are present but their composition is broken.

This connects directly to the "imposter intelligence" post angle: Can LLMs understand concepts they cannot apply?, Does supervised fine-tuning actually improve reasoning quality?, and Do foundation models learn world models or task-specific shortcuts?. All describe the same meta-pattern: surface metrics certify capability that internal structure analysis would disqualify.

The practical implication for model evaluation: passing compositional generalization tests does not guarantee robust compositional reasoning. Evaluation under distribution shift, perturbation, and novel recombination is required to distinguish genuine compositionality from fractured representations that happen to contain the right features.

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Why do models fail under distribution shift if accuracy metrics stay high?Can steering vectors prove that representations are genuinely organized?Does scaling data automatically produce compositional reasoning or just better feature encoding?What test distinguishes genuine compositionality from fractured feature presence?
Original note title

identical performance metrics can mask fundamentally different internal representations — feature linear decodability does not guarantee representational organization