Halliday & Matthiessen (2014: 396):
In all such nominal expressions where Head and Thing are not conflated although both are clearly present, what is being construed is a phenomenon that from one point of view appears as a single entity and from another point of view as two. Such expressions have their basis in the concrete realms of our experience, such as cups and coffee; they then become an extremely rich resource for construing the virtual entities that make up so much of the environment of our adult existence.