> True! I suppose I was thinking about a 'strong' form of linear representations, which is something like: features are represented by linear combinations of neurons that display the same repulsion-geometries as observed in Toy Models, but that's not what you're saying / that's me jumping a step too far.

Note this happens in "uniform superposition". In reality, we're almost certainly in very non-uniform superposition.

One key term to look for is "feature manifolds" or "multi-diemsnional features". Some discussion here: https://transformer-circuits.pub/2024/july-update/index.html...

(Note that the term "strong linear representation" is becoming a term of art in the literature referring to the idea that all features are linear, rather than just most or some.)

> I want to make sure I'm getting my terminology right -- why does superposition necessarily require the linear representation hypothesis? Or, to be more specific, does [individual neurons being used in combination with other neurons to represent more features than neurons] necessarily require [features are linear compositions of neurons]?

When you say "individual neurons being used in combination with other neurons to represent more features than neurons", that's a way one might _informally_ talk about superposition, but doesn't quite capture the technical nuance. So it's hard to know the full scope of what you intend. All kinds of crazy things are possible if you allow non-linear features, and it's not necessarily clear what a feature would mean.

Superposition, in the narrow technical sense of exploiting compressed sensing / high-dimensional spaces, requires linear representations and sparsity.