,g,,. THE GRAMMAR OF SCIENCE. 305 



only be divergent from each other, but divergent from the perceptual 

 experience from which each started. This divergent abstraction, as we 

 may term it, may be illustrated by an analogy. Two investigators 

 study the same substance, say carbon disulphide, a dense, colourless 

 liquid. One abstracts the sulphur and formulates its properties, 

 neglecting the carbon : the other neglects the sulphur and investi- 

 gates the carbon, formulating its properties. The resulting pro- 

 perties in the two cases are different, or even contradictory. One 

 obtains a yellow solid with these properties ; the other a black solid 

 with those properties ; and the phenomenal substance with which 

 each started is neither the one nor the other, but a colourless liquid ! 

 So the geometrician obtains a geometrical conception of continuous 

 surface, neglecting atomic structure : and the physicist obtains a 

 molecular conception of discrete particles. But the perceptual 

 conception, as such, has neither a continuous boundary ^5 idealised in 

 geometry, nor a molecular constitution as idealised in physics. And to 

 predicate these idealised conceptions of " perceptual bodies," there- 

 fore, leads to antinomy and confusion ; the moral of which is that 

 we must not introduce among the concepts of one line of investigation 

 the concepts which result from another line of investigation. 



The next chapter, on The Geometry of Motion, starts by describing 

 motion as " the mixed mode under which all perception takes place." 

 This way of regarding the problems of motion is the natural outcome 

 of the conception of space and time as modes of perception. How far 

 the discussion of the geometry of motion in this chapter, and of Matter 

 and the Laws of Motion in succeeding chapters, will be satisfactory 

 to specialists in physics, it is not for me to say. Regarding the 

 matter merely from the general standpoint of natural science, I must 

 confess that it appears to me more simple, and more scientifically 

 accurate, to regard matter and motion as frankly objective and 

 (perceptually) external. This is, however, not Professor Pearson's 

 view. " If we confine ourselves," he says, " to the field of logical 

 inference, we see in the phenomenal universe not matter in motion, 

 but sense-impressions and changes of sense-impressions, co-existence 

 and sequence, correlation and routine." Now although direct per- 

 ception does not give us abstract matter in ideal motion, it does most 

 certainly give us particular moving things, animals and men going 

 from place to place, unsupported bodies falling towards the earth, the 

 balloon ascending through the air, the clouds drifting across the face 

 of the moon. All these are for adult perception occurrences in the 

 external phenomenal world. If the psychologist, as the result of his 

 analytic thought, reaches the conception of " sense-impressions and 

 changes of sense-impressions," well and good ; but this does not alter 

 one whit the fact that for perception the movements we observe are 

 occurrences in the world of phenomena. It is perfectly true that the 

 sense-impression is that which starts the perceptual process and calls 

 the percept into being. But it is equally true that the sense- 



