i MENTAL EVOLUTION 7 



which one mass movement gives rise to another in accord- 

 ance with uniform law comes suddenly to a dead stop. 

 There is some particular movement of some particular 

 particles which sets up no further movement, but instead 

 of so doing has as its effect a modification of a totally 

 different kind of thing called Consciousness. This thing 

 being set to work arrives in its turn at a point where it, 

 not being itself a mass in motion, nevertheless sets a mole- 

 cular mass in motion, and so presently brings about what 

 we recognise as an act of the individual. 



3. This account involves so violent a discontinuity in the 

 causal process that most thinkers shrink from it, and take 

 refuge in some theory of Parallelism. According to this 

 view there is no breach of physical or mechanical con- 

 tinuity. If we could master the whole details of the neural 

 process we should find that in the most complex delibera- 

 tion, as in the simplest reflex, they run their course in the 

 fixed groove of mechanical law. Motion gives rise to 

 motion within the brain cells and along the brain fibres in 

 strict accordance with the Conservation of Momentum. 

 But certain motions of certain kinds of molecule are for 

 reasons unknown to us accompanied by definite changes in 

 that which we know as consciousness, the relation being so 

 intricately adjusted that there is a point to point correspon- 

 dence between molecular and conscious modifications. The 

 two streams flow, so to say, not merely side by side, but 

 in one bed. Each, considered internally, exhibits perfect 

 uniformity of sequence, and together they form the whole 

 which is the internal life and external behaviour of the 

 conscious thinking animal. 



This theory in turn has many points of difficulty. But 

 what concerns us principally here is to note one of its main 

 consequences. The phenomena of consciousness, meta- 

 physical theories apart, are limited to animal bodies, and 

 moreover to certain processes only which occur within 

 animal bodies. The physical, on the other hand, is every- 

 where. Thus the process to which a physical stimulus 

 first gives rise and which ultimately issues in a physical 

 action is physical throughout. On the mechanical plane 

 its continuity is unbroken, and its self-determination is 



