A theory of ordered structures in which every definable subset of the line (one-dimensional domain) is a finite union of points and intervals; o-minimality enforces a strong geometric tameness on definable sets.

Principle

Require that definable subsets of the domain in one variable are simple—finite unions of points and intervals—so higher-dimensional definable sets inherit tame geometric and topological properties via cell decomposition and dimension theory.

Demonstration

The theory of the ordered real field is o-minimal: every definable subset of the real line is a finite union of points and open/closed intervals, which yields tame geometry and allows tools like cell decomposition and definable continuity.

Misapplication

Assuming o-minimality follows from any mild ordering or from the absence of pathological combinatorics; many ordered structures lack o-minimality and one cannot infer o-minimality merely from NIP or stability.

Consequence

O-minimality yields powerful consequences: definable sets have finite topological complexity, dimensions behave predictably, definable functions are piecewise continuous and differentiable under mild expansions, and one obtains strong geometric and measure-theoretic control.

Reversal

The opposite are ordered theories where some definable subset of the line has fractal or highly oscillatory behaviour, or encodes arbitrary discrete patterns—these lack o-minimal tameness and admit wild definable sets.

Boundary

Applies to first-order expansions of ordered structures and concerns one-dimensional definable sets as a starting point; it excludes theories where order interacts with richer combinatorics or non-definable completeness, and does not generalize straightforwardly to non-ordered languages.

Semantic Tension

Tension exists with NIP and stability: o-minimality is stronger and geometric in nature—every o-minimal theory is NIP but not conversely; o-minimality requires order-theoretic regularity beyond mere combinatorial tameness.

Synthesis

O-minimality is the ordering-based tameness condition that demands one-dimensional definable sets be finite unions of points and intervals, which propagates to tame multi-dimensional geometry and strong regularity of definable functions.