From Groups to Rings: Causal Evidence for Algebraic Decomposition in Grokked Transformers

Prior work has shown that grokked Transformers implement discrete Fourier transforms or group character representations for modular arithmetic. We unify these findings under the Wedderburn--Artin decomposition: using interchange intervention accuracy (IIA), a causal method stronger than ablation, we show that grokked models decompose computation along the Wedderburn components of the target algebra. Across 11 commutative algebras over $\F_p$ ($p = 2,3,5,7$)---including 6 with nontrivial Jacobson radical---all grokked models achieve raw IIA $\geq 0.97$. When models predict incorrectly, errors remain compartmentalized by component ($3.8\times$ chance), confirming that independence is structural, not a byproduct of accuracy. Training dynamics reveal that Wedderburn alignment emerges synchronously with grokking. For non-commutative groups, models exhibit \emph{selective} Wedderburn alignment; non-commutativity raises a capacity threshold that larger models overcome.