category/neighbor

Not the boundary between a thing and its absence but between one class and the class immediately adjacent — thin enough that a small shift crosses it. Averaging is the mechanism: a process collapsing many instances toward the most probable configuration erodes exactly the differences that hold neighbouring categories apart, which is entropy operating on classification and the reason -ness looks the way it does. The boundary fails not because anyone contests it but because the operation underneath tends toward the least differentiated result.