Title: Enforcing Axioms for AI Alignment under Loss-Based Rules
Primary area: alignment, fairness, safety, privacy, and societal considerations
Keywords: Social Choice, AI Alignment, Reinforcement Learning from Human Feedback, Constitutional AI

Abstract: Recent alignment methods for large language models, most notably reinforcement learning from human feedback (RLHF), often train an auxiliary reward model to minimize a loss function on binary preference data over model responses. We study a theoretical setting inspired by principle-guided methods such as Constitutional AI, in which a small set of principles (e.g., helpfulness, toxicity) act as “voters” that guide binary comparisons---such as preferring the less toxic response. We model these principles as linear functionals over an embedding space of responses, a simplifying assumption motivated by the Linear Representation Hypothesis---concepts are linear directions in representation space---a useful first-order approximation in practice.
In this \emph{linear social choice model}, Ge et al. (2024) showed that an optimal linear reward model can violate Pareto optimality (PO): From the principles-as-voters lens, this means a response A can be less helpful and more toxic than B, yet still receive a higher reward. We analyze axiomatic violations in the linear social choice setting and probe the robustness of negative results under realistic assumptions. We show that added expressivity does not resolve the issue: polynomial reward models can still fail PO. We then offer a pragmatic alternative showing that when the data uniformly covers the embedding space, broad classes of loss-based rules in the limit exactly recover the axiomatic guarantees. This yields a recipe for constitutional-style alignment with provable guarantees: enforce balanced coverage \emph{via dataset design} to restore axiomatic guarantees without abandoning standard training pipelines.