We start with the phenomena, and select which ones we want to try to understand first. For this reduced set of phenomena, we try to construct theories that give an adequate and concise account of them. In the course of time, we try to enlarge the set of phenomena we study. Our goal is to capture as large an area of phenomena as possible, with as simple a set of theories as possible. Whether there are intrinsic limits to the realization of this program, is an open question .
Materialism is the view that all that occurs, occurs in dependence on material causes.
Without such a view, it would be very difficult to engage in physics, since the outcome of any experiment could be interpreted as being the result of non-physical causes. The notion that physics is a complete system, covering all of reality, is a very daring one indeed. It is really only during this century, that such a notion can be defended seriously. According to relativity theory, it includes energy as well, and according to quantum theory, we can no longer talk about uniquely defined states of being. Actions act, without anything extra required.