The perceptual judgment which is present in the completed recognition of physical objects introduces the notion of hypothetical perceptions by percipient objects, located for an indefinite number of hypothetical percipient events. In other words, it is a judgment on the events of the universe as being favourable active conditions for the perception of the physical object, granting the correspondingly favourable percipient events. There are an indefinite number of such percipient events, actual or imaginary. The characters of events as active conditions are to be inferred from their adjustment to these innumerable possibilities of perception of each physical object.
25.2 Also in another way physical objects are the links connecting nature as perceived with nature as conditioning its own perception. Physical objects are often termed the causes of the perception of sense-objects, other than the sense-objects which are among their own components. For example, the telescope is the cause of the astronomer's seeing the star. But a physical object is a cause only in an indirect mediate sense. The fact of the telescope being in the right position at the right time was an active condition for the astronomer's sight of the star. Now this fact is an event which is a 'situation' of the telescope. Thus in our experience the situations of physical objects are discovered to be active conditions for the perception of sense-objects. In this way a knowledge of the characters of events, in so far as they are active conditions, can be observed and inferred; and the passage from perception to causation is effected.
25.3 At once the question arises, In what terms are the characters of the conditioning events to be expressed? The unanimous answer has been, that the expression is to be in terms of 'matter,' or—allowing for the more subtle ether—in terms of 'material.' In so deciding none of the distinctions made above have been consistently held in view. The result has been the persistent lapses into confusion which have been exhibited in a brief abstract in the first part of this enquiry.
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.
25.6 In terms of space and time (as derived by the method of extensive abstraction) the situation of a physical object shrinks into its spatial position at an instant together with its associated motion. Also an event occupied by an electron shrinks into the position at an instant of the electric charge forming its nucleus, together with its associated motion. But the quantitative charge is entirely devoid of character apart from its associated field; it expresses the character of the occupied events which is due to their relation to the electron. Its permanence of quantity reflects the permanence which is recognised in the electron, considered for itself alone.
25.7 The 'unoccupied' events possess a definite character expressive of the reign of law in the creative advance of nature, i.e. in the passage of events. This type of character of events unoccupied by the electron is also shared by the occupied events. It expresses the rôle of the electron as an agency in the passage of events. In fact the electron is nothing else than the expression of certain permanent recognisable features in this creative advance.
Thus the character of event e which it receives from electron