Decomposition of multiports is used to show that the nine basic elements of bond graphs are based on the two basic principles of physics, viz., the energy conservation principle and the positive entropy production principle, and the fact that each model has to be separated from its environment that can still influence its behavior. These three concepts have to be conceptually interconnected which leads to the concept of a power continuous junction structure. This junction structure can be decomposed itself, which finally leads to nine basic concepts.