Concept of arrangement in an $N$-body quantum system

We discuss the concept of ``arrangement'', traditionally found in the context of few-body rearrangement collisions, in a more general context of an $N$-body quantum system. We show that for an $N$-body quantum system with attractive interactions that can bind the constituent particles, the concept of arrangement provides both a necessary and an important basis for understanding its complexity and the general structure of its Hilbert space. The concept is a necessary part of a foundation for a more complete understanding of $N$-body quantum systems, especially those made of atoms and molecules.