61.2 It is necessary however to avoid a misunderstanding; the causal character of an event is not merely a function of the apparent character of that event. It is in truth a function of the apparent characters of all events, though in general the apparent character of that event—or of an associated event of somewhat later date—is the dominant element in the formation of the function. For example, a quantity determined by measurement is a relation of the apparent character of the event to the apparent characters of other events. But it is the dominance of the apparent character which in practice makes the discovery of the causal character generally possible; for it assigns the situation of the causal character. This dominance is merely a practical aid to the discovery of causal characters and has in it no element of necessity. Indeed as causal characters are progressively discovered, scientific theory assigns causal characters to events which are destitute of apparent character—namely the events forming the ether in empty space and time. 61.3 So far the explanation of causal characters has exhibited them as the outcome and issue from apparent characters, whereas the causal idea, which is that of science, requires the causal characters should be the origin of the apparent characters. We have to seek the reason for this inversion of ideas. Causal characters are much simpler than apparent characters; are more permanent than apparent characters; and depend almost entirely on the event itself, involving other events only (in general) as passive conditions providing the necessary background of a whole continuum of nature. The climb from the sense-object to the perceptual object, and from the perceptual object to the scientific object, and from the complex scientific object (such as the molecule) to the (temporally, in a stage of science) ultimate scientific object (such as the electron) is a steady pursuit of simplicity, permanence, and self-sufficiency, combined with the essential attribute of adequacy for the purpose of defining the apparent characters. 61.4 The relations of sense-objects to their situations are complex in the extreme, requiring reference to percipient events and transmitting events. Apart from some discovery of laws of nature regulating the associations of sense-objects, it is impossible by unintelligent unsorted perception to form any concept of the character of an event from the sense-objects which might be situated there for percipients suffering from any normal or abnormal perceptions.