Matter has been classified into the various kinds of matter which are the chemical substances; thence the atomic theory of matter has been established; and thence some form of electromagnetic theory of molecules is emerging. It is in the last degree unlikely that the present form of this theory will represent its final stage. All novel theories emerge with a childlike simplicity which they ultimately shed. But, apart from specific details, it can as little be doubted that in its main concepts the theory is true. 25.4 We will accordingly pass by the elaborate task of tracking down and interpreting intermediate stages of scientific concepts—important though they are—and pass at once to the consideration of molecules and electrons. The characters of events in their capacity of active conditioning events for sense-objects are expressed by their relations to scientific objects. Scientific objects are not directly perceived, they are inferred by reason of their capacity to express these characters, namely, they express how it is that events are conditions. In other words they express the causal characters of events. 25.5 At the present epoch the ultimate scientific objects are electrons. Each such scientific object has its special relation to each event in nature. Events as thus related to a definite electron are called the 'field' of that object. The relations of the object to different parts of the field are interconnected; and, when the relationship of the object to certain parts of the field is known, its relationship to the remaining parts can be calculated. As here defined the field of an electron extends through all time and all space, each event bearing a certain character expressed by its relation to the electron. As in the case of other objects, the electron is an atomic unity, only mediately in space and in time by reason of its specific relations to events. This field is divisible into two parts, namely, the 'occupied' events and the 'unoccupied' events. The occupied event corresponds to the situation of a physical object. In order to express these relations of an electron to events with sufficient simplicity, the method of extensive abstraction [cf. Part III] has to be employed. The success of this method depends on the principle of convergence to simplicity with diminution of extent. The result is to separate off the temporal and spatial properties of events. The relations of electrons to events can be expressed in terms of spatial positions and spatial motions at all instants throughout the whole of time.