Physical objects and scientific objects are causal characters which are discussed in Chapter XVI. Also sense-objects and perceptual objects are the apparent characters discussed in that chapter. But the separation between the apparent and the causal must not be over stressed: it is relative to a deliberately limited point of view. The whole of 23 would be made clearer by the use of the term 'ingression' for the complex relation of a sense-object to the other factors of nature which make up a social entity in process of realisation. The over-simplification involved in the Aristotelian concept of 'quality-subject' has obscured the analysis of ingression. Also 24 is confused by a wavering between the 'class-theory' of perceptual objects and the 'control-theory' of physical objects, and by the confusion between perceptual and physical objects. I do not hold the class-theory now in any form, and was endeavouring in this book to get away from it. In Chapter XVI the 'causal character' is identical with the perceptual object so far as immediate perception is concerned, with the physical object so far as further discrimination of the significance of immediate appearance is concerned, and with scientific objects so far as more detailed analysis is concerned. Note IV. The attempt in 33 to define a duration merely by means of its unlimitedness is a failure. In a note to the Concept of Nature, I point out that there is an analogous unlimitedness through time, corresponding to the spatial unlimitedness of a duration. Both unlimitednesses arise from the uniform significance of spatial extension for one, and of temporal extension for the other. Thus there is a temporal unlimitedness arising from a stationary event [cf. 41] in a definite space-time system. A point-track is the outcome of such an unlimitedness deprived of all spatial extension. But of course a point-track is a mere limit arrived at by the method of extensive abstraction. But I still hold to 35.4. Note V. In 47 the concept of normality is explained with unnecessary elaboration. Let and be two intersecting moments belonging to diverse space-time systems and . Thus intersection of and is an instantaneous plane which lies in the instantaneous three-dimensional moments and . Let be an event-particle [i.e. an instantaneous point] in it . Then there is a point-track through , belonging to the space-time system , and an analogous point-track belonging to .