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THE POPULAR SCIENCE MONTHLY. 



in the sensiferous apparatus are continuous with, and similar to, those 

 which take place in the external world.* But, with the sensoriura, mat- 

 ter and motion come to an end ; while phenomena of another order, or 

 immaterial states of consciousness, make their appearance. How is the 

 relation between the material and the immaterial phenomena to be con- 

 ceived ? This is the metaphysical problem of problems, and the solu- 

 tions which have been suggested have been made the corner-stones of 

 systems of philosophy. Three mutually irreconcilable readings of the 

 riddle have been offered. 



The first is, that an immaterial substance of mind exists ; and that 

 it is affected by the mode of motion of the sensorium in such a way as 

 to give rise to the sensation. 



The second is, that the sensation is a direct effect of the mode of 

 motion of the sensorium, brought about without the intervention of any 

 substance of mind. 



The third is, that the sensation is neither directly, nor indirectly, an 

 effect of the mode of motion of the sensorium, but that it has an inde- 

 pendent cause. Properly speaking, therefore, it is not an effect of the 

 motion of the sensorium, but a concomitant of it. 



As none of these hypotheses is capable of even an approximation to 

 demonstration, it is almost needless to remark that they have been sev- 

 erally held with tenacity and advocated with passion. I do not think 

 it can be said of any of the three that it is inconceivable, or that it can 

 be assumed on a priori grounds to be impossible. 



Consider the first, for example; an immaterial substance is perfectly 

 conceivable. In fact, it is obvious that, if we possessed no sensations 



* The following diagrammatic scheme may help to elucidate the theory of sensation: 

 Mediate Knowledge 



Sensiferous Apparatus 



Immediate 

 Knowledge 



Objects of Sense 



Hypothetical 



Substance of 



Matter 



Receptive Transmissive Sensificatory 

 (Sense-Organ) (Nerve) (Sensorium) 



Sensations and 



other States of 



Consciousness 



Hypothetical 



Substance of 



Mind 



Physical World 



Mental World 



Not Self 



Self 



Non-Ego or Object. 



Ego or Subject 



Immediate Knowledge is confined to states of consciousness, or, in other words, to the 

 phenomena of mind. Knowledge of the physical world, or of one's own body and of ob- 

 jects external to it, is a system of beliefs or judgments based on the sensations. The 

 term " self" is applied not only to the series of mental phenomena which constitute the 

 ego, but to the fragment of the physical world which is their constant concomitant. The 

 corporeal self, therefore, is part of the non-ego ; and is objective in relation to the ego as 

 subject. 



