3 1 8 Heredity. 



is to be understood, and on what grounds it rests ; for our own 

 part, we neither accept nor reject it. 



If we are to accept it, it must be verifiable by experience, or 

 demonstrable by logic. Experimental verification would consist 

 in showing that it agrees with all the facts, and that it can be 

 brought entirely under their control ; but it is impossible to 

 show any 'such thing. Logical demonstration would consist in 

 showing that this one hypothesis, exclusive of all others, 

 explains the facts ; but this demonstration per absurdum is im- 

 possible. 



If we are to reject it, the hypothesis must involve some logical 

 contradiction ; but this is not the case. It is true that it is difficult 

 to understand how no-thought can become thought, but without 

 attempting to explain this, we may bear in mind that this transition 

 is progressive, and that life and thought share in common this 

 essential character, that they are a correspondence produced by a 

 series of actions and reactions. Moreover, this evolutional genesis 

 of the forms of thought, which the doctrine of development applies 

 to the species, is admitted by all as applying to the individual. 

 The individual cannot think (in the proper sense of the word) 

 until his brain is developed ; and if thought, in its true sense, 

 possessed of all its constituent forms, comes into being in an 

 instant which is doubtful we do not see why this bright flash in 

 the night of the unconscious should not have lighted up the species 

 also, at some definite instant To say that the objects of the con- 

 stituent forms of thought space, time, causality could not have 

 modified the brain, because they have no concrete existence in 

 nature, as have a stone or a dog, is not to present a difficulty ; for 

 if, with Leibnitz, we regard them as relations it is quite natural that 

 the brain should be modified, not only by things, but by the rela- 

 tions between things. 



These two opposite theories the one regarding thought as the 

 essential causality to which nature is a secondary causality, and 

 the other regarding nature as the essential causality and thought 

 as secondary might perhaps be reconciled by admitting the 

 identity of mechanism and logic, of intelligence in nature and 

 intelligence in thought. We have already alluded to this doctrine, 

 but this is not the place to set it forth. 



