Why Quantum Theory

This article investigates one of the fundamental issues con-fronting a field that investigates quantum interaction; namely why is it necessary? The need to investigate an interaction using a quantum formalism is argued to arise when the sys-tem under study is sufficiently complex. In particular, if the system is displaying contextual behaviour then a quantum ap-proach often incorporates this behaviour very naturally. Thus, a way in which much of the disparate work in the field of quantum interaction can be both justified to the broader com-munity and eventually unified is presented. The nature of contextual behaviour and its relationship to nonlocality is ex-plored. An in-depth example investigating some of these is-sues is left to (Bruza et al. 2008). Interactio