Granted that both are equally real, different ways have been adopted of stating their difference. One way is that of G. F. Stout (Proceedings of the Aristotelian Society, N.S. vol. iv., 1903-4, p. 153) that "the difference lies in their respective relation to the interaction of material things." The executive order of the material world can be expressed only in terms of the primary and not in terms of the secondary properties of matter. In Bergson's doc trine (Matter and Memory, ch. iv.) red differs from the corre sponding vibrations in the tempo at which the experience is taken by the mind : what at a slower rhythm of duree may be apprehended as mechanical vibrations at a faster rhythm is con densed into colour.
But in the important recent philosophy of A. N. Whitehead, although the relative position of the two sets is not discussed as such, the traditional priority of the primaries would seem almost to be reversed in favour of the secondaries. The secondaries are, of course, real. In a happy phrase Whitehead has effectually destroyed the "representationism" inherited from Locke and Descartes by "protesting against the bifurcation of nature into two systems of reality," the one physical, which is not directly known, and the other "which is the byplay of the mind" (Con cept of Nature, 1920). The world in this philosophy is a world of events, and the simplest events into which the total event which is "the passage of nature" can be resolved are described as "situations" into which "eternal objects," like red or sweet, which are not events, make "ingression." The perception of sense objects implies a multiple relation into which enter the "percipient event" which is a bodily state, the "situation," the "eternal ob ject" and the surrounding conditions (p. 152). (Compare his Science and the Modern World, pp. 99-102.) The reality of secondary qualities is here not in doubt. The relative position of the primaries and secondaries is not so clear. For space and time on this doctrine are relational, relations be tween events as thus fully qualified by ingression of eternal objects; and accordingly constructions are framed to describe in terms of concrete events such conceptions as points, areas, volumes, etc. ; and the great merit of this procedure is that it starts from concrete events instead of from conceptual entities like points. It is possible thus to define a point by means of all the sets of concrete extensions (e.g., red patches) by which we can approach it. Now, to come to the present question, since space and time are relations between events, they are logically posterior in rank to the events themselves; and it would, seem to follow that primary qualities such as geometrical figures, which are enumerated under the head of eternal objects (Science and the Modern World, p. 146), are posterior to the secondary quali ties which are situated in the events. At least the two sets of
qualities appear to be on a different footing. This is, however, not the author's statement but an inference of the writer's, which may be mistaken. We may add that the omission of any analysis or explanation of the vague conception of "relation" makes the whole subject obscure.
A different though allied doctrine, that of the writer (Space, Time and Deity), leaves the primary qualities with their tradi tional priority, while at the same time raising difficulties of its own. According to this view the stuff of the world is space-time itself, that is, pure events, and the qualities or objects, which on Whitehead's doctrine are ingredient into events from the be ginning, are said to emerge historically as the web of events within the whole space-time assumes certain complexities of configura tion. Primary qualities, such as shapes or numbers, arise within space-time at the earliest level of existence. Subsequently these spatio-temporal configurations assume a certain complexity and we have matter or at least sub-matter. At a higher level of com plexity there "emerge" certain material or submaterial con figurations, complexes in the end of space-time, which are those conditions of bodies of which we have become aware as colour or taste. The notion of Emergence (q.v.) indicates the fact that at certain critical points in the development of the spatio-tem poral world, new qualities appear, which are based upon the lower level of existence, and while also equivalent to the lower level complex are qualified by a new character. So, to take an example from a higher stage of history, a certain complex of chemical and mechanical processes is endowed with the quality life ; in the same way as a certain complex of purely spatio-tem poral configurations becomes submaterial. Emergence is a term applied by this writer to the large critical novelties only; by Lloyd Morgan it is applied more freely to any change that can be called a change of character. (Whitehead uses the term dif ferently. Since events from the outset are characterized by qualities through the ingression of objects, he speaks naturally of the emergence not of a new quality or "eternal object" but of a new thing through the ingression of a fresh complex of eternal objects.) On this second view, then, secondary qualities emerge from primary ones when those primary qualities, as in material or submaterial things, reach a certain degree and kind of com plexity—e.g., when certain motions occur in the body which are propagated in the form of light waves. The grave difficulties, which need not be concealed, in this general doctrine lie in its basis, in its use of the notion of pure event without quality, and its assumption without investigation of geometrical ideas such as point and line.